diff --git a/messages/de.json b/messages/de.json
index e5629cc51..6425dcc38 100644
--- a/messages/de.json
+++ b/messages/de.json
@@ -6891,6 +6891,8 @@
       "recoveryGapLagSymptom": "Dir ging es {days} Tage besser, bevor deine erfassten Symptome abklangen.",
       "recoveryGapLeadSymptom": "Deine erfassten Symptome klangen {days} Tage ab, bevor du Genesung vermerktest.",
       "recoveryGapSame": "Deine Werte normalisierten sich am selben Tag, an dem es dir besser ging.",
+      "sleepContextMore": "Während dieser Episode hast du deutlich mehr geschlafen als sonst (etwa {hours} Std./Nacht).",
+      "sleepContextLess": "Während dieser Episode hast du deutlich weniger geschlafen als sonst (etwa {hours} Std./Nacht).",
       "redFlagTitle": "Genauer ansehen",
       "redFlagSpo2": "Deine Sauerstoffsättigung blieb mehrere Tage niedrig. Wenn das erneut auftritt, suche ärztliche Hilfe.",
       "redFlagFever": "Du hattest anhaltend Fieber. Wenn das erneut auftritt, suche ärztliche Hilfe.",
diff --git a/messages/en.json b/messages/en.json
index a44932a9f..e010dba9a 100644
--- a/messages/en.json
+++ b/messages/en.json
@@ -6891,6 +6891,8 @@
       "recoveryGapLagSymptom": "You felt better {days} days before your logged symptoms eased.",
       "recoveryGapLeadSymptom": "Your logged symptoms eased {days} days before you marked recovery.",
       "recoveryGapSame": "Your numbers settled the same day you felt better.",
+      "sleepContextMore": "During this episode you slept noticeably more than usual (about {hours}h/night).",
+      "sleepContextLess": "During this episode you slept noticeably less than usual (about {hours}h/night).",
       "redFlagTitle": "Worth a closer look",
       "redFlagSpo2": "Your oxygen saturation stayed low for several days. If this recurs, seek medical care.",
       "redFlagFever": "You ran a sustained fever. If this recurs, seek medical care.",
diff --git a/messages/es.json b/messages/es.json
index e8f6b9456..4f7cdf34a 100644
--- a/messages/es.json
+++ b/messages/es.json
@@ -6891,6 +6891,8 @@
       "recoveryGapLagSymptom": "Te sentiste mejor {days} días antes de que cedieran tus síntomas registrados.",
       "recoveryGapLeadSymptom": "Tus síntomas registrados cedieron {days} días antes de marcar la recuperación.",
       "recoveryGapSame": "Tus valores se estabilizaron el mismo día en que te sentiste mejor.",
+      "sleepContextMore": "Durante este episodio dormiste notablemente más de lo habitual (unas {hours} h/noche).",
+      "sleepContextLess": "Durante este episodio dormiste notablemente menos de lo habitual (unas {hours} h/noche).",
       "redFlagTitle": "Conviene revisarlo",
       "redFlagSpo2": "Tu saturación de oxígeno se mantuvo baja varios días. Si se repite, busca atención médica.",
       "redFlagFever": "Tuviste fiebre sostenida. Si se repite, busca atención médica.",
diff --git a/messages/fr.json b/messages/fr.json
index 1c58b4827..e669ee63e 100644
--- a/messages/fr.json
+++ b/messages/fr.json
@@ -6891,6 +6891,8 @@
       "recoveryGapLagSymptom": "Tu t'es senti mieux {days} jours avant que tes symptômes consignés s'apaisent.",
       "recoveryGapLeadSymptom": "Tes symptômes consignés se sont apaisés {days} jours avant que tu notes la guérison.",
       "recoveryGapSame": "Tes valeurs se sont stabilisées le jour même où tu t'es senti mieux.",
+      "sleepContextMore": "Pendant cet épisode, tu as dormi nettement plus que d'habitude (environ {hours} h/nuit).",
+      "sleepContextLess": "Pendant cet épisode, tu as dormi nettement moins que d'habitude (environ {hours} h/nuit).",
       "redFlagTitle": "À examiner de plus près",
       "redFlagSpo2": "Ta saturation en oxygène est restée basse plusieurs jours. Si cela se reproduit, consulte un médecin.",
       "redFlagFever": "Tu as eu une fièvre persistante. Si cela se reproduit, consulte un médecin.",
diff --git a/messages/it.json b/messages/it.json
index 6778c0ec7..e68135dfa 100644
--- a/messages/it.json
+++ b/messages/it.json
@@ -6891,6 +6891,8 @@
       "recoveryGapLagSymptom": "Ti sei sentito meglio {days} giorni prima che i sintomi registrati si attenuassero.",
       "recoveryGapLeadSymptom": "I tuoi sintomi registrati si sono attenuati {days} giorni prima di segnare la guarigione.",
       "recoveryGapSame": "I tuoi valori si sono stabilizzati lo stesso giorno in cui ti sei sentito meglio.",
+      "sleepContextMore": "Durante questo episodio hai dormito molto più del solito (circa {hours} h/notte).",
+      "sleepContextLess": "Durante questo episodio hai dormito molto meno del solito (circa {hours} h/notte).",
       "redFlagTitle": "Da guardare più da vicino",
       "redFlagSpo2": "La tua saturazione di ossigeno è rimasta bassa per diversi giorni. Se si ripete, rivolgiti a un medico.",
       "redFlagFever": "Hai avuto febbre persistente. Se si ripete, rivolgiti a un medico.",
diff --git a/messages/pl.json b/messages/pl.json
index 638f8a520..54ae78cff 100644
--- a/messages/pl.json
+++ b/messages/pl.json
@@ -6891,6 +6891,8 @@
       "recoveryGapLagSymptom": "Poczułeś się lepiej {days} dni przed ustąpieniem zapisanych objawów.",
       "recoveryGapLeadSymptom": "Twoje zapisane objawy ustąpiły {days} dni przed oznaczeniem wyzdrowienia.",
       "recoveryGapSame": "Twoje wartości ustabilizowały się tego samego dnia, gdy poczułeś się lepiej.",
+      "sleepContextMore": "Podczas tego epizodu spałeś zauważalnie więcej niż zwykle (około {hours} godz./noc).",
+      "sleepContextLess": "Podczas tego epizodu spałeś zauważalnie mniej niż zwykle (około {hours} godz./noc).",
       "redFlagTitle": "Warto przyjrzeć się bliżej",
       "redFlagSpo2": "Twoje wysycenie tlenem pozostawało niskie przez kilka dni. Jeśli się powtórzy, zasięgnij pomocy medycznej.",
       "redFlagFever": "Miałeś utrzymującą się gorączkę. Jeśli się powtórzy, zasięgnij pomocy medycznej.",
diff --git a/src/components/illness/illness-correlation-card.tsx b/src/components/illness/illness-correlation-card.tsx
index 57e937154..4edec9d0b 100644
--- a/src/components/illness/illness-correlation-card.tsx
+++ b/src/components/illness/illness-correlation-card.tsx
@@ -41,6 +41,11 @@ function DeviationRow({ d }: { d: IllnessVitalDeviation }) {
   );
 }
 
+/** Round asleep-minutes to a friendly hours figure (one decimal). */
+function hoursFromMinutes(minutes: number): string {
+  return (Math.round((minutes / 60) * 10) / 10).toString();
+}
+
 function CorrelationBody({ value }: { value: IllnessCorrelationValue }) {
   const { t } = useTranslations();
   const gap = value.recoveryGapDays;
@@ -48,6 +53,9 @@ function CorrelationBody({ value }: { value: IllnessCorrelationValue }) {
   // the symptoms ("…before your symptoms eased"); otherwise the existing
   // vital-driven phrasing. Clinically calm — observation, never prediction.
   const symptomDriven = value.gapDriverType === "FUNCTIONAL_IMPACT";
+  // Sleep-as-context: a neutral observation subordinate to the gap, withheld by
+  // the engine on thin data — never a recovery claim, never a second gap.
+  const sleep = value.sleepContext;
 
   return (
     <div className="space-y-5">
@@ -90,6 +98,16 @@ function CorrelationBody({ value }: { value: IllnessCorrelationValue }) {
                   )
                 : t("illness.correlation.recoveryGapSame")}
           </p>
+          {sleep ? (
+            <p className="text-muted-foreground mt-1.5 text-xs">
+              {t(
+                sleep.deltaMinutes > 0
+                  ? "illness.correlation.sleepContextMore"
+                  : "illness.correlation.sleepContextLess",
+                { hours: hoursFromMinutes(Math.abs(sleep.deltaMinutes)) },
+              )}
+            </p>
+          ) : null}
         </div>
       ) : null}
 
diff --git a/src/components/illness/types.ts b/src/components/illness/types.ts
index 581dcd3fd..4f87580e5 100644
--- a/src/components/illness/types.ts
+++ b/src/components/illness/types.ts
@@ -111,6 +111,19 @@ export interface IllnessRedFlag {
   days: number;
 }
 
+/**
+ * A neutral sleep-as-context observation for the episode — slept more / less
+ * than usual — surfaced ALONGSIDE the gap, never part of the recovery-gap
+ * number. Null when the sleep data is too thin or the delta sub-floor.
+ */
+export interface SleepContext {
+  baselineMeanMinutes: number;
+  episodeMeanMinutes: number;
+  /** `episode − baseline` asleep minutes (positive = slept more than usual). */
+  deltaMinutes: number;
+  nightsCounted: number;
+}
+
 export interface IllnessCorrelationValue {
   episodeId: string;
   preOnset: IllnessVitalDeviation[];
@@ -126,6 +139,11 @@ export interface IllnessCorrelationValue {
    */
   gapDriverType: string | null;
   redFlags: IllnessRedFlag[];
+  /**
+   * Sleep-as-context observation, or null when withheld (thin data / sub-floor
+   * delta). Additive — never part of the headline recovery-gap.
+   */
+  sleepContext: SleepContext | null;
 }
 
 /** The flat `Derived<T>` wire shape the correlation route returns. */
diff --git a/src/lib/illness/__tests__/correlation-read.test.ts b/src/lib/illness/__tests__/correlation-read.test.ts
index 8850bc813..1bbd00b9a 100644
--- a/src/lib/illness/__tests__/correlation-read.test.ts
+++ b/src/lib/illness/__tests__/correlation-read.test.ts
@@ -65,6 +65,9 @@ vi.mock("@/lib/rollups/measurement-coverage", () => ({
 vi.mock("@/lib/rollups/measurement-read-wmy", () => ({
   readBestGranularityRollups: rollup.readBestGranularityRollups,
 }));
+vi.mock("@/lib/rollups/measurement-read", () => ({
+  loadUserSourcePriority: vi.fn(async () => null),
+}));
 
 import { computeEpisodeCorrelation } from "../correlation-read";
 import { ILLNESS_SCAN_TYPES } from "../correlation";
@@ -302,3 +305,120 @@ describe("computeEpisodeCorrelation — contamination-guard read window", () =>
     }
   });
 });
+
+describe("computeEpisodeCorrelation — sleep-as-context read", () => {
+  it("reconstructs baseline + episode nights and surfaces the observation, deduping multi-source nights", async () => {
+    rollup.probeRollupCoverage.mockResolvedValue(
+      new Map<string, boolean>(
+        ILLNESS_SCAN_TYPES.map((t) => [String(t), false]),
+      ),
+    );
+    rollup.readBestGranularityRollups.mockResolvedValue(null);
+
+    // A banded RHR vital (flat-ish at 55) clears the engine coverage floor.
+    const rhrRows: Array<{ value: number; measuredAt: Date }> = [];
+    {
+      let cursor = Date.parse("2025-12-05T12:00:00Z");
+      const jit = [-2, -1, 0, 1, 2];
+      for (let i = 0; i < 40; i++) {
+        rhrRows.push({
+          value: 55 + jit[i % jit.length],
+          measuredAt: new Date(cursor),
+        });
+        cursor += 24 * 60 * 60 * 1000;
+      }
+    }
+
+    // Sleep rows. Baseline nights ~420 min (7h); episode nights ~510 min
+    // (8.5h) → +90 min. The episode 2026-01-11 night is DOUBLE-WRITTEN by two
+    // sources (WHOOP + Apple Health); the canonical reconstruction must count
+    // it ONCE, not sum it to ~1020 min and inflate the delta.
+    // A "night" is one asleep block whose wake-day is the local calendar day.
+    type SleepRow = {
+      value: number;
+      measuredAt: Date;
+      sleepStage: null;
+      source: string;
+      deviceType: string | null;
+    };
+    const sleepRows: SleepRow[] = [];
+    const asleepNight = (
+      wakeDay: string,
+      minutes: number,
+      source: string,
+    ): SleepRow => ({
+      // The block ENDS at 07:00Z on the wake-day; one ASLEEP sample of `minutes`.
+      value: minutes,
+      measuredAt: new Date(`${wakeDay}T07:00:00Z`),
+      sleepStage: null,
+      source,
+      deviceType: source,
+    });
+    // Baseline nights (well before the pre-onset lookback start 2026-01-03).
+    for (const day of [
+      "2025-12-20",
+      "2025-12-21",
+      "2025-12-22",
+      "2025-12-23",
+      "2025-12-24",
+      "2025-12-25",
+    ]) {
+      sleepRows.push(asleepNight(day, 420, "WHOOP"));
+    }
+    // Episode nights (active span ≥ onset 2026-01-10).
+    sleepRows.push(asleepNight("2026-01-10", 510, "WHOOP"));
+    // Double-written night — same wake-day, two writers.
+    sleepRows.push(asleepNight("2026-01-11", 510, "WHOOP"));
+    sleepRows.push(asleepNight("2026-01-11", 510, "APPLE_HEALTH"));
+    sleepRows.push(asleepNight("2026-01-12", 510, "WHOOP"));
+
+    db.measurement.findMany.mockImplementation(
+      async ({
+        where,
+      }: {
+        where: {
+          type: string;
+          measuredAt: { gte: Date; lt?: Date; lte?: Date };
+        };
+      }) => {
+        const from = where.measuredAt.gte.getTime();
+        const to =
+          where.measuredAt.lt?.getTime() ??
+          where.measuredAt.lte?.getTime() ??
+          NOW.getTime();
+        if (where.type === "RESTING_HEART_RATE") {
+          return rhrRows.filter(
+            (r) =>
+              r.measuredAt.getTime() >= from && r.measuredAt.getTime() <= to,
+          );
+        }
+        if (where.type === "SLEEP_DURATION") {
+          return sleepRows.filter(
+            (r) =>
+              r.measuredAt.getTime() >= from && r.measuredAt.getTime() <= to,
+          );
+        }
+        return [];
+      },
+    );
+
+    const episode = {
+      id: "ep-sleep",
+      onsetAt: new Date("2026-01-10T08:00:00Z"),
+      resolvedAt: null as Date | null,
+      lifecycle: "ACUTE",
+    };
+
+    const out = await computeEpisodeCorrelation("u1", episode, "UTC", NOW);
+    expect(out.status).toBe("ok");
+    if (out.status !== "ok") return;
+    const sleep = out.value.sleepContext;
+    expect(sleep).not.toBeNull();
+    expect(sleep?.baselineMeanMinutes).toBe(420);
+    // The double-written 01-11 night is counted ONCE → episode mean ≈ 510, not
+    // a doubled ~680 that summing two writers would produce.
+    expect(sleep?.episodeMeanMinutes).toBe(510);
+    expect(sleep?.deltaMinutes).toBe(90);
+    expect(sleep?.nightsCounted).toBe(3);
+  });
+});
diff --git a/src/lib/illness/__tests__/correlation.test.ts b/src/lib/illness/__tests__/correlation.test.ts
index fd5a855b3..e2fe3a3d6 100644
--- a/src/lib/illness/__tests__/correlation.test.ts
+++ b/src/lib/illness/__tests__/correlation.test.ts
@@ -20,7 +20,9 @@ import {
   isAdverseDeviation,
   MIN_BASELINE_DAYS,
   MIN_EPISODE_COVERAGE_DAYS,
+  SLEEP_CONTEXT_MIN_DELTA_MINUTES,
   type IllnessCorrelationInput,
+  type SleepNightPoint,
   type SymptomBurdenPoint,
   type VitalDayPoint,
 } from "../correlation";
@@ -810,3 +812,343 @@ describe("computeIllnessCorrelation — symptom-burden return track", () => {
     ).toBeUndefined();
   });
 });
+
+describe("computeIllnessCorrelation — relapse-aware return (last sustained)", () => {
+  it("reports the LAST sustained return when the vital relapses mid-episode", () => {
+    // Deviate 01-10, settle in-band 01-13..01-15 (a 3-day run that the OLD
+    // first-return rule would have called the return), re-deviate 01-16..01-18,
+    // then settle again 01-20..01-22 and hold. felt-better 01-14. The honest
+    // answer is the SECOND settle (01-20), not the first — the relapse pushes
+    // the return later and extends the gap.
+    const type: MeasurementType = "RESTING_HEART_RATE";
+    const baselineDays = jitteredBaseline(55, 1, 21, "2026-01-02");
+    const episodeDays: VitalDayPoint[] = [
+      { day: "2026-01-10", mean: 75 }, // first deviation
+      { day: "2026-01-12", mean: 74 },
+      { day: "2026-01-13", mean: 55 }, // first settle (old return)
+      { day: "2026-01-14", mean: 55 },
+      { day: "2026-01-15", mean: 55 }, // 3-day in-band run
+      { day: "2026-01-16", mean: 75 }, // RELAPSE
+      { day: "2026-01-17", mean: 74 },
+      { day: "2026-01-18", mean: 73 },
+      { day: "2026-01-20", mean: 55 }, // final settle start
+      { day: "2026-01-21", mean: 55 },
+      { day: "2026-01-22", mean: 55 }, // holds to end
+    ];
+    const out = computeIllnessCorrelation(
+      input({
+        window: {
+          onsetDay: "2026-01-10",
+          feltBetterDay: "2026-01-14",
+          lifecycle: "ACUTE",
+        },
+        series: [{ type, baselineDays, episodeDays }],
+      }),
+    );
+    expect(out.status).toBe("ok");
+    if (out.status !== "ok") return;
+    expect(out.value.returns[0]?.returnedDay).toBe("2026-01-20");
+    // Gap = 01-20 − 01-14 = +6 (the old first-return would have given −1).
+    expect(out.value.recoveryGapDays).toBe(dayDiff("2026-01-14", "2026-01-20"));
+    expect(out.value.recoveryGapDays).toBe(6);
+  });
+
+  it("reports the LAST sustained symptom return when the curve relapses", () => {
+    // Parity with the vital track on the symptom curve: impact eases to 0 for 3
+    // logged days, flares back to 2, eases to 0 again for 3 logged days → the
+    // return is the SECOND easing, not the first.
+    const rhr: MeasurementType = "RESTING_HEART_RATE";
+    const rhrBaseline = jitteredBaseline(55, 1, 21, "2026-01-02");
+    const rhrFlat: VitalDayPoint[] = [
+      { day: "2026-01-10", mean: 55 },
+      { day: "2026-01-11", mean: 55 },
+      { day: "2026-01-12", mean: 55 },
+      { day: "2026-01-13", mean: 55 },
+      { day: "2026-01-14", mean: 55 },
+    ];
+    const symptomBurden: SymptomBurdenPoint[] = [
+      { day: "2026-01-10", impact: 3 },
+      { day: "2026-01-12", impact: 2 },
+      { day: "2026-01-13", impact: 0 }, // first easing
+      { day: "2026-01-14", impact: 0 },
+      { day: "2026-01-15", impact: 0 }, // 3 logged in-band days
+      { day: "2026-01-16", impact: 2 }, // FLARE
+      { day: "2026-01-18", impact: 0 }, // final easing start
+      { day: "2026-01-19", impact: 0 },
+      { day: "2026-01-20", impact: 0 }, // 3 logged in-band days, holds
+    ];
+    const out = computeIllnessCorrelation(
+      input({
+        window: {
+          onsetDay: "2026-01-10",
+          feltBetterDay: "2026-01-14",
+          lifecycle: "ACUTE",
+        },
+        series: [
+          { type: rhr, baselineDays: rhrBaseline, episodeDays: rhrFlat },
+        ],
+        symptomBurden,
+      }),
+    );
+    expect(out.status).toBe("ok");
+    if (out.status !== "ok") return;
+    const sym = out.value.returns.find(
+      (r) => r.type === FUNCTIONAL_IMPACT_RETURN_KEY,
+    );
+    expect(sym?.returnedDay).toBe("2026-01-18");
+    expect(sym?.gapDays).toBe(dayDiff("2026-01-14", "2026-01-18"));
+    expect(out.value.recoveryGapDays).toBe(4);
+  });
+
+  it("withholds when the final in-band run is too short after a relapse", () => {
+    // Deviate, settle, relapse, then only 2 in-band days to the window end —
+    // the final run is shorter than RETURN_STABILITY_DAYS, so no return is
+    // fabricated off the too-short tail.
+    const type: MeasurementType = "RESTING_HEART_RATE";
+    const baselineDays = jitteredBaseline(55, 1, 21, "2026-01-02");
+    const episodeDays: VitalDayPoint[] = [
+      { day: "2026-01-10", mean: 75 }, // deviation
+      { day: "2026-01-12", mean: 55 }, // settle
+      { day: "2026-01-13", mean: 55 },
+      { day: "2026-01-14", mean: 55 }, // 3-day run
+      { day: "2026-01-16", mean: 75 }, // RELAPSE
+      { day: "2026-01-17", mean: 74 },
+      { day: "2026-01-19", mean: 55 }, // only 2 in-band days to end
+      { day: "2026-01-20", mean: 55 },
+    ];
+    const out = computeIllnessCorrelation(
+      input({
+        window: {
+          onsetDay: "2026-01-10",
+          feltBetterDay: "2026-01-14",
+          lifecycle: "ACUTE",
+        },
+        series: [{ type, baselineDays, episodeDays }],
+      }),
+    );
+    expect(out.status).toBe("ok");
+    if (out.status !== "ok") return;
+    expect(out.value.returns[0]?.returnedDay).toBeNull();
+    expect(out.value.recoveryGapDays).toBeNull();
+  });
+
+  it("picks the FINAL settle across multiple relapses", () => {
+    // settle → flare → settle → flare → settle: the last contiguous in-band
+    // span wins regardless of how many intervening cycles.
+    const type: MeasurementType = "RESTING_HEART_RATE";
+    const baselineDays = jitteredBaseline(55, 1, 21, "2026-01-02");
+    const episodeDays: VitalDayPoint[] = [
+      { day: "2026-01-10", mean: 75 }, // deviation
+      { day: "2026-01-11", mean: 55 }, // settle 1
+      { day: "2026-01-12", mean: 55 },
+      { day: "2026-01-13", mean: 55 },
+      { day: "2026-01-14", mean: 75 }, // flare 1
+      { day: "2026-01-15", mean: 55 }, // settle 2
+      { day: "2026-01-16", mean: 55 },
+      { day: "2026-01-17", mean: 55 },
+      { day: "2026-01-18", mean: 75 }, // flare 2
+      { day: "2026-01-20", mean: 55 }, // FINAL settle start
+      { day: "2026-01-21", mean: 55 },
+      { day: "2026-01-22", mean: 55 }, // holds to end
+    ];
+    const out = computeIllnessCorrelation(
+      input({
+        window: {
+          onsetDay: "2026-01-10",
+          feltBetterDay: "2026-01-14",
+          lifecycle: "ACUTE",
+        },
+        series: [{ type, baselineDays, episodeDays }],
+      }),
+    );
+    expect(out.status).toBe("ok");
+    if (out.status !== "ok") return;
+    expect(out.value.returns[0]?.returnedDay).toBe("2026-01-20");
+    expect(out.value.recoveryGapDays).toBe(6);
+  });
+
+  it("returns null when the episode ends out-of-band after a relapse", () => {
+    // Deviate, settle, relapse, never resolve (ends elevated) → no sustained
+    // final return → null gap. Honest: it did not finally settle in-window.
+    const type: MeasurementType = "RESTING_HEART_RATE";
+    const baselineDays = jitteredBaseline(55, 1, 21, "2026-01-02");
+    const episodeDays: VitalDayPoint[] = [
+      { day: "2026-01-10", mean: 75 }, // deviation
+      { day: "2026-01-12", mean: 55 }, // settle
+      { day: "2026-01-13", mean: 55 },
+      { day: "2026-01-14", mean: 55 }, // 3-day run
+      { day: "2026-01-16", mean: 75 }, // RELAPSE
+      { day: "2026-01-18", mean: 74 },
+      { day: "2026-01-20", mean: 73 }, // still elevated at the end
+    ];
+    const out = computeIllnessCorrelation(
+      input({
+        window: {
+          onsetDay: "2026-01-10",
+          feltBetterDay: "2026-01-14",
+          lifecycle: "ACUTE",
+        },
+        series: [{ type, baselineDays, episodeDays }],
+      }),
+    );
+    expect(out.status).toBe("ok");
+    if (out.status !== "ok") return;
+    expect(out.value.returns[0]?.returnedDay).toBeNull();
+    expect(out.value.recoveryGapDays).toBeNull();
+  });
+});
+
+describe("computeIllnessCorrelation — sleep-as-context observation", () => {
+  // A banded RHR vital clears the engine coverage floor in every case; the
+  // sleep context is computed independently from the night arrays.
+  const rhr: MeasurementType = "RESTING_HEART_RATE";
+  const rhrBaseline = jitteredBaseline(55, 1, 21, "2026-01-02");
+  const rhrFlat = flatBaseline(55, 5, "2026-01-15");
+
+  /** N baseline nights at `minutes`, ending the day before onset. */
+  function nights(
+    minutes: number,
+    count: number,
+    endDay: string,
+  ): SleepNightPoint[] {
+    const out: SleepNightPoint[] = [];
+    let cursor = Date.parse(`${endDay}T00:00:00Z`);
+    for (let i = 0; i < count; i++) {
+      out.unshift({
+        day: new Date(cursor).toISOString().slice(0, 10),
+        asleepMinutes: minutes,
+      });
+      cursor -= 24 * 60 * 60 * 1000;
+    }
+    return out;
+  }
+
+  it("surfaces a slept-more observation when the episode delta clears the floor", () => {
+    // Baseline ~420 min (7h), episode ~510 min (8.5h) → +90 min, well past the
+    // 30-min floor. Episode nights are inside the active span.
+    const out = computeIllnessCorrelation(
+      input({
+        series: [
+          { type: rhr, baselineDays: rhrBaseline, episodeDays: rhrFlat },
+        ],
+        baselineNights: nights(420, 6, "2026-01-02"),
+        episodeNights: [
+          { day: "2026-01-10", asleepMinutes: 510 },
+          { day: "2026-01-11", asleepMinutes: 505 },
+          { day: "2026-01-12", asleepMinutes: 515 },
+        ],
+      }),
+    );
+    expect(out.status).toBe("ok");
+    if (out.status !== "ok") return;
+    expect(out.value.sleepContext).not.toBeNull();
+    expect(out.value.sleepContext?.baselineMeanMinutes).toBe(420);
+    expect(out.value.sleepContext?.deltaMinutes).toBeGreaterThanOrEqual(
+      SLEEP_CONTEXT_MIN_DELTA_MINUTES,
+    );
+    expect(out.value.sleepContext?.nightsCounted).toBe(3);
+    // It never touches the recovery-gap.
+    expect(out.value.recoveryGapDays).toBeNull();
+  });
+
+  it("withholds when the delta is below the magnitude floor", () => {
+    // Baseline 420, episode 430 → +10 min, sub-floor jitter → no observation.
+    const out = computeIllnessCorrelation(
+      input({
+        series: [
+          { type: rhr, baselineDays: rhrBaseline, episodeDays: rhrFlat },
+        ],
+        baselineNights: nights(420, 6, "2026-01-02"),
+        episodeNights: [
+          { day: "2026-01-10", asleepMinutes: 430 },
+          { day: "2026-01-11", asleepMinutes: 425 },
+          { day: "2026-01-12", asleepMinutes: 435 },
+        ],
+      }),
+    );
+    expect(out.status).toBe("ok");
+    if (out.status !== "ok") return;
+    expect(out.value.sleepContext).toBeNull();
+  });
+
+  it("withholds when too few episode nights are scorable", () => {
+    const out = computeIllnessCorrelation(
+      input({
+        series: [
+          { type: rhr, baselineDays: rhrBaseline, episodeDays: rhrFlat },
+        ],
+        baselineNights: nights(420, 6, "2026-01-02"),
+        episodeNights: [
+          { day: "2026-01-10", asleepMinutes: 520 },
+          { day: "2026-01-11", asleepMinutes: 525 }, // only 2 episode nights
+        ],
+      }),
+    );
+    expect(out.status).toBe("ok");
+    if (out.status !== "ok") return;
+    expect(out.value.sleepContext).toBeNull();
+  });
+
+  it("withholds when the baseline night count is too thin", () => {
+    const out = computeIllnessCorrelation(
+      input({
+        series: [
+          { type: rhr, baselineDays: rhrBaseline, episodeDays: rhrFlat },
+        ],
+        baselineNights: nights(420, 3, "2026-01-02"), // only 3 baseline nights
+        episodeNights: [
+          { day: "2026-01-10", asleepMinutes: 520 },
+          { day: "2026-01-11", asleepMinutes: 525 },
+          { day: "2026-01-12", asleepMinutes: 515 },
+        ],
+      }),
+    );
+    expect(out.status).toBe("ok");
+    if (out.status !== "ok") return;
+    expect(out.value.sleepContext).toBeNull();
+  });
+
+  it("surfaces a slept-less observation with a negative delta", () => {
+    const out = computeIllnessCorrelation(
+      input({
+        series: [
+          { type: rhr, baselineDays: rhrBaseline, episodeDays: rhrFlat },
+        ],
+        baselineNights: nights(480, 6, "2026-01-02"),
+        episodeNights: [
+          { day: "2026-01-10", asleepMinutes: 360 },
+          { day: "2026-01-11", asleepMinutes: 370 },
+          { day: "2026-01-12", asleepMinutes: 350 },
+        ],
+      }),
+    );
+    expect(out.status).toBe("ok");
+    if (out.status !== "ok") return;
+    expect(out.value.sleepContext?.deltaMinutes).toBeLessThanOrEqual(
+      -SLEEP_CONTEXT_MIN_DELTA_MINUTES,
+    );
+  });
+
+  it("excludes pre-onset nights from the episode mean", () => {
+    // A pre-onset night (before onsetDay 2026-01-10) must not count toward the
+    // episode mean — only the active-span nights do.
+    const out = computeIllnessCorrelation(
+      input({
+        series: [
+          { type: rhr, baselineDays: rhrBaseline, episodeDays: rhrFlat },
+        ],
+        baselineNights: nights(420, 6, "2026-01-02"),
+        episodeNights: [
+          { day: "2026-01-08", asleepMinutes: 999 }, // pre-onset — must be dropped
+          { day: "2026-01-10", asleepMinutes: 510 },
+          { day: "2026-01-11", asleepMinutes: 510 },
+          { day: "2026-01-12", asleepMinutes: 510 },
+        ],
+      }),
+    );
+    expect(out.status).toBe("ok");
+    if (out.status !== "ok") return;
+    expect(out.value.sleepContext?.episodeMeanMinutes).toBe(510);
+    expect(out.value.sleepContext?.nightsCounted).toBe(3);
+  });
+});
diff --git a/src/lib/illness/__tests__/retrospective.test.ts b/src/lib/illness/__tests__/retrospective.test.ts
index f9dc38125..3cb4d062e 100644
--- a/src/lib/illness/__tests__/retrospective.test.ts
+++ b/src/lib/illness/__tests__/retrospective.test.ts
@@ -15,6 +15,30 @@ import {
   MIN_TYPICAL_GAP_MAGNITUDE_DAYS,
   type RetrospectiveEpisode,
 } from "../retrospective";
+import { computeIllnessCorrelation, type VitalDayPoint } from "../correlation";
+
+/** A baseline with a non-zero, stable MAD (mirrors the correlation suite). */
+function jitteredBaseline(
+  center: number,
+  jitter: number,
+  days: number,
+  endDay: string,
+): VitalDayPoint[] {
+  const out: VitalDayPoint[] = [];
+  let cursor = Date.parse(`${endDay}T00:00:00Z`);
+  const offsets = [-jitter, -jitter / 2, 0, jitter / 2, jitter];
+  for (let i = 0; i < days; i++) {
+    out.unshift({
+      day: new Date(cursor).toISOString().slice(0, 10),
+      mean: center,
+    });
+    cursor -= 24 * 60 * 60 * 1000;
+  }
+  return out.map((p, i) => ({
+    ...p,
+    mean: center + offsets[i % offsets.length],
+  }));
+}
 
 function ep(over: Partial<RetrospectiveEpisode>): RetrospectiveEpisode {
   return {
@@ -207,4 +231,68 @@ describe("summarizeIllnessRetrospective", () => {
     ]);
     expect(out.typicalRecoveryGapDays).toBe(-3);
   });
+
+  it("threads the larger last-return gap through the cross-episode median", () => {
+    // Integration guard for the relapse-aware (last-sustained) return change:
+    // one episode relapses mid-course, so its ENGINE-computed gap grows from
+    // the old first-return value (−1) to the last-return value (+6). The
+    // retrospective consumes that engine number verbatim — confirm the larger
+    // value pulls the cross-episode median up rather than the stale first
+    // return. No retrospective code changes; this guards the integration.
+    const baselineDays = jitteredBaseline(55, 1, 21, "2026-01-02");
+    const relapseEpisode: VitalDayPoint[] = [
+      { day: "2026-01-10", mean: 75 }, // first deviation
+      { day: "2026-01-13", mean: 55 }, // first settle (old return)
+      { day: "2026-01-14", mean: 55 },
+      { day: "2026-01-15", mean: 55 }, // 3-day run
+      { day: "2026-01-16", mean: 75 }, // RELAPSE
+      { day: "2026-01-18", mean: 73 },
+      { day: "2026-01-20", mean: 55 }, // final settle start
+      { day: "2026-01-21", mean: 55 },
+      { day: "2026-01-22", mean: 55 }, // holds to end
+    ];
+    const engine = computeIllnessCorrelation({
+      episodeId: "relapse",
+      window: {
+        onsetDay: "2026-01-10",
+        feltBetterDay: "2026-01-14",
+        lifecycle: "ACUTE",
+      },
+      series: [
+        {
+          type: "RESTING_HEART_RATE",
+          baselineDays,
+          episodeDays: relapseEpisode,
+        },
+      ],
+      source: "DAY",
+      now: new Date("2026-02-01T00:00:00Z"),
+    });
+    expect(engine.status).toBe("ok");
+    if (engine.status !== "ok") return;
+    // Last-return = 01-20, gap = +6 (not the old first-return −1).
+    expect(engine.value.recoveryGapDays).toBe(6);
+
+    const out = summarizeIllnessRetrospective([
+      ep({
+        id: "relapse",
+        recoveryGapDays: engine.value.recoveryGapDays,
+        gapMeasurementDays: engine.coverage.historyDays,
+        gapReturnTypes: ["RESTING_HEART_RATE"],
+      }),
+      ep({
+        id: "b",
+        recoveryGapDays: 4,
+        gapReturnTypes: ["RESTING_HEART_RATE"],
+      }),
+      ep({
+        id: "c",
+        recoveryGapDays: 5,
+        gapReturnTypes: ["RESTING_HEART_RATE"],
+      }),
+    ]);
+    // Median of [6, 4, 5] = 5 — the relapse episode's grown gap is in the mix.
+    expect(out.typicalRecoveryGapDays).toBe(5);
+    expect(out.gapDriverType).toBe("RESTING_HEART_RATE");
+  });
 });
diff --git a/src/lib/illness/correlation-read.ts b/src/lib/illness/correlation-read.ts
index ca05de559..08b5840bf 100644
--- a/src/lib/illness/correlation-read.ts
+++ b/src/lib/illness/correlation-read.ts
@@ -31,6 +31,8 @@ import { readBestGranularityRollups } from "@/lib/rollups/measurement-read-wmy";
 import { probeRollupCoverage } from "@/lib/rollups/measurement-coverage";
 import { dayKeyForUserTz } from "@/lib/measurements/consolidation-tz";
 import { resolveUserTimezone } from "@/lib/measurements/consolidation-base";
+import { reconstructNights } from "@/lib/insights/derived/sleep-score";
+import { loadUserSourcePriority } from "@/lib/rollups/measurement-read";
 import type { Derived } from "@/lib/insights/derived/types";
 import {
   BASELINE_WINDOW_DAYS,
@@ -39,6 +41,7 @@ import {
   computeIllnessCorrelation,
   type DayLogFeverPoint,
   type IllnessCorrelationValue,
+  type SleepNightPoint,
   type SymptomBurdenPoint,
   type VitalSeries,
 } from "./correlation";
@@ -96,15 +99,20 @@ export async function computeEpisodeCorrelation(
     : null;
 
   // One coverage probe shared across every vital read (pool-contention
-  // mitigation — the same pattern the derived route uses).
-  const coverage = await probeRollupCoverage(userId);
+  // mitigation — the same pattern the derived route uses). The source priority
+  // feeds the canonical sleep-night writer-dedup (same ladder every sleep
+  // surface uses), resolved once.
+  const [coverage, sleepPriorityJson] = await Promise.all([
+    probeRollupCoverage(userId),
+    loadUserSourcePriority(userId),
+  ]);
 
   // Attempt every scan type under a bounded concurrency cap. The two
   // windows per type (baseline + episode) are independent reads, so they
   // run paired rather than serially (halving the per-type round-trips).
   // The day-log fever read shares the same fan-out budget.
   const limit = pLimit(VITAL_SCAN_CONCURRENCY);
-  const [perType, dayLogFever, symptomBurden] = await Promise.all([
+  const [perType, dayLogFever, symptomBurden, sleepNights] = await Promise.all([
     Promise.all(
       ILLNESS_SCAN_TYPES.map((type) =>
         limit(async () => {
@@ -134,6 +142,14 @@ export async function computeEpisodeCorrelation(
     ),
     limit(() => readDayLogFever(episode.id, preOnsetStart, end, tz)),
     limit(() => readDayLogSymptomBurden(episode.id, preOnsetStart, end, tz)),
+    limit(() =>
+      readEpisodeSleepNights(
+        userId,
+        { baselineStart, baselineEnd, preOnsetStart, end },
+        tz,
+        sleepPriorityJson,
+      ),
+    ),
   ]);
 
   const series: VitalSeries[] = [];
@@ -170,6 +186,8 @@ export async function computeEpisodeCorrelation(
     series,
     dayLogFever,
     symptomBurden,
+    baselineNights: sleepNights.baselineNights,
+    episodeNights: sleepNights.episodeNights,
     source,
     now,
   });
@@ -331,3 +349,75 @@ async function readDayLogSymptomBurden(
   }
   return points.sort((a, b) => (a.day < b.day ? -1 : a.day > b.day ? 1 : 0));
 }
+
+/**
+ * Reconstruct per-night asleep totals over the well baseline window AND the
+ * episode window for the sleep-as-context observation. Reuses the canonical
+ * `reconstructNights` engine wholesale (session-clustering, local-wake-day
+ * keying, multi-source writer-dedup — a WHOOP + Apple Health night is counted
+ * ONCE) so the figures match every other sleep surface. The night's `night`
+ * key is ALREADY the local wake-day string, so it joins the engine's
+ * onset/feltBetter day-space directly — no extra tz conversion.
+ *
+ * Two windows mirror the vital reads' contamination-guard seam:
+ *   baselineNights : [baselineStart, baselineEnd)  → the user's well baseline
+ *   episodeNights  : [preOnsetStart, end]          → the episode span
+ *
+ * Each is a single bounded `findMany` over the raw per-stage SLEEP_DURATION
+ * rows; the engine withholds the observation entirely on thin data.
+ */
+async function readEpisodeSleepNights(
+  userId: string,
+  windows: {
+    baselineStart: Date;
+    baselineEnd: Date;
+    preOnsetStart: Date;
+    end: Date;
+  },
+  tz: string,
+  priorityJson: unknown,
+): Promise<{
+  baselineNights: SleepNightPoint[];
+  episodeNights: SleepNightPoint[];
+}> {
+  const select = {
+    value: true,
+    measuredAt: true,
+    sleepStage: true,
+    source: true,
+    deviceType: true,
+  } as const;
+
+  const [baselineRows, episodeRows] = await Promise.all([
+    prisma.measurement.findMany({
+      where: {
+        userId,
+        type: "SLEEP_DURATION" satisfies MeasurementType,
+        deletedAt: null,
+        measuredAt: { gte: windows.baselineStart, lt: windows.baselineEnd },
+      },
+      orderBy: { measuredAt: "asc" },
+      select,
+    }),
+    prisma.measurement.findMany({
+      where: {
+        userId,
+        type: "SLEEP_DURATION" satisfies MeasurementType,
+        deletedAt: null,
+        measuredAt: { gte: windows.preOnsetStart, lte: windows.end },
+      },
+      orderBy: { measuredAt: "asc" },
+      select,
+    }),
+  ]);
+
+  const toPoints = (rows: typeof baselineRows): SleepNightPoint[] =>
+    reconstructNights(rows, tz, priorityJson)
+      .filter((n) => n.asleepMinutes > 0)
+      .map((n) => ({ day: n.night, asleepMinutes: n.asleepMinutes }));
+
+  return {
+    baselineNights: toPoints(baselineRows),
+    episodeNights: toPoints(episodeRows),
+  };
+}
diff --git a/src/lib/illness/correlation.ts b/src/lib/illness/correlation.ts
index 7756c7c33..da2d51aab 100644
--- a/src/lib/illness/correlation.ts
+++ b/src/lib/illness/correlation.ts
@@ -83,6 +83,20 @@ export const FUNCTIONAL_IMPACT_RETURN_KEY = "FUNCTIONAL_IMPACT" as const;
 export const FUNCTIONAL_IMPACT_ADVERSE_FLOOR = 1;
 /** Minimum episode days with ANY vital coverage before the gap is asserted. */
 export const MIN_EPISODE_COVERAGE_DAYS = 4;
+/**
+ * Minimum scorable baseline nights before the sleep-context observation is
+ * trusted (mirrors the sleep-debt engine's `minNights` floor). Below this the
+ * "usual" asleep figure is too fragile to compare against.
+ */
+export const SLEEP_CONTEXT_MIN_BASELINE_NIGHTS = 4;
+/** Minimum scorable episode nights before the sleep-context line surfaces. */
+export const SLEEP_CONTEXT_MIN_EPISODE_NIGHTS = 3;
+/**
+ * Minimum |episode − baseline| asleep-minutes delta before the sleep-context
+ * line is shown. Day-to-day jitter below this floor is not narrated as a
+ * finding (honest withholding, never a fabricated observation).
+ */
+export const SLEEP_CONTEXT_MIN_DELTA_MINUTES = 30;
 
 /**
  * Per-metric adverse direction — which way a reading moves when the body is
@@ -184,6 +198,21 @@ export interface SymptomBurdenPoint {
   impact: number;
 }
 
+/**
+ * One reconstructed night's asleep total, keyed by the local WAKE-DAY (the same
+ * `YYYY-MM-DD` day-space the engine's onset/feltBetter markers live in — a
+ * canonical `NightSummary.night`). The caller reconstructs nights from the raw
+ * per-stage SLEEP_DURATION rows (writer-deduped, session-clustered) and passes
+ * the asleep totals in; the engine never touches raw rows. Used ONLY for the
+ * sleep-context observation, NEVER as a recovery-gap return track.
+ */
+export interface SleepNightPoint {
+  /** Local wake-day key, `YYYY-MM-DD`. */
+  day: string;
+  /** Asleep minutes for the night (canonical, multi-source-deduped). */
+  asleepMinutes: number;
+}
+
 /** The dates the engine reasons over, all `YYYY-MM-DD` local day keys. */
 export interface EpisodeWindow {
   /** Onset day. */
@@ -216,6 +245,20 @@ export interface IllnessCorrelationInput {
    * passive-vital-thin episode. Optional.
    */
   symptomBurden?: SymptomBurdenPoint[];
+  /**
+   * Reconstructed per-night asleep totals over the user's WELL baseline window
+   * (the span ending before the pre-onset lookback). Their median is the user's
+   * usual asleep figure the episode is compared against. Optional — absent /
+   * thin → no sleep-context observation. NEVER feeds the recovery-gap.
+   */
+  baselineNights?: SleepNightPoint[];
+  /**
+   * Reconstructed per-night asleep totals over the episode window (`onset −
+   * lookback` through end). Compared against the baseline median as a neutral
+   * CONTEXT observation (slept more / less than usual), never a return track and
+   * never in the gap median. Optional — absent / thin → no observation.
+   */
+  episodeNights?: SleepNightPoint[];
   /** Provenance source the dominant read resolved against. */
   source: "DAY" | "live" | "none";
   /** Compute time (injected for deterministic tests). */
@@ -276,6 +319,25 @@ export function isAdverseDeviation(
   );
 }
 
+/**
+ * A neutral sleep-context observation for the episode — the user's median
+ * asleep minutes over the well baseline vs the mean over the episode window. A
+ * pure OBSERVATION ("you slept more / less than usual"), never a recovery
+ * return, never in the gap median, never a causal/recovery claim. Null when the
+ * sleep data is too thin (below the night-count floors) or the delta is below
+ * the magnitude floor — honest withholding, never a fabricated finding.
+ */
+export interface SleepContext {
+  /** Median asleep minutes over the well baseline window. */
+  baselineMeanMinutes: number;
+  /** Mean asleep minutes over the episode window. */
+  episodeMeanMinutes: number;
+  /** `episode − baseline` asleep minutes (positive = slept more than usual). */
+  deltaMinutes: number;
+  /** Scorable episode nights the observation is built from (transparency). */
+  nightsCounted: number;
+}
+
 export interface IllnessCorrelationValue {
   episodeId: string;
   /** "How did it announce itself" — notable pre-onset deviations. */
@@ -317,6 +379,13 @@ export interface IllnessCorrelationValue {
    * recurs, seek care"), NEVER reassure. Empty when nothing tripped.
    */
   redFlags: IllnessRedFlag[];
+  /**
+   * Sleep-as-context observation — slept more / less than usual during the
+   * episode — or null when the sleep data is too thin or the delta sub-floor.
+   * A neutral observation surfaced ALONGSIDE the gap, NEVER a return track and
+   * NEVER part of the headline recovery-gap number. Optional/additive.
+   */
+  sleepContext: SleepContext | null;
 }
 
 export interface IllnessRedFlag {
@@ -508,7 +577,7 @@ export function computeIllnessCorrelation(
     //    deviation (which yielded a spurious negative gap). Excluded for
     //    CHRONIC_ONGOING (no recovered date by design).
     if (firstDeviationIndex >= 0 && window.lifecycle !== "CHRONIC_ONGOING") {
-      const returnedDay = firstStableReturn(
+      const returnedDay = lastStableReturn(
         active,
         center,
         spread,
@@ -593,6 +662,15 @@ export function computeIllnessCorrelation(
     fullHistoryDays: Math.max(MIN_EPISODE_COVERAGE_DAYS, 14),
   });
 
+  // Sleep-as-context — a neutral observation surfaced alongside the gap, NEVER a
+  // return track and NEVER in the recovery-gap median. Withholds (null) on thin
+  // data or a sub-floor delta.
+  const sleepContext = computeSleepContext(
+    input.baselineNights ?? [],
+    input.episodeNights ?? [],
+    window,
+  );
+
   return buildOk<IllnessCorrelationValue>({
     value: {
       episodeId: input.episodeId,
@@ -608,6 +686,7 @@ export function computeIllnessCorrelation(
       feltBetterDay: window.feltBetterDay,
       gapDriverType: gapDriverType === null ? null : String(gapDriverType),
       redFlags,
+      sleepContext,
     },
     coverage,
     confidence,
@@ -616,13 +695,22 @@ export function computeIllnessCorrelation(
 }
 
 /**
- * First day in `active` (chronological), starting at `fromIndex`, where the
- * vital is in-band AND stays in-band for the next `RETURN_STABILITY_DAYS`
- * observed days. Null when it never settles. "In-band" = |deviation| <
- * NOTABLE_SD. `fromIndex` pins the search to AFTER the first deviation so an
- * early in-band run (the run-up to the illness) is never mistaken for a return.
+ * Start of the FINAL sustained in-band run in `active` (chronological) at/after
+ * `fromIndex` — the day the vital *finally* settled and held to the end of the
+ * observed span. "In-band" = |deviation| < NOTABLE_SD. Null when it never
+ * settles, or when it ends out-of-band (still elevated at the last reading), or
+ * when the final in-band run is shorter than `RETURN_STABILITY_DAYS` observed
+ * days. `fromIndex` pins the search to AFTER the first deviation so an early
+ * in-band run (the run-up to the illness) is never mistaken for a return.
+ *
+ * This is the relapse-aware "last sustained return": an episode that settles,
+ * re-deviates (a mid-episode flare), and settles again reports the LAST settle.
+ * The change is monotone — a last return is always >= the first return day — so
+ * any series that settles ONCE (first == last) is unaffected. Multiple relapses
+ * collapse to the same rule: the final contiguous in-band span wins by
+ * construction, no special-casing.
  */
-function firstStableReturn(
+function lastStableReturn(
   active: VitalDayPoint[],
   center: number,
   spread: number,
@@ -632,13 +720,16 @@ function firstStableReturn(
     day: p.day,
     in: Math.abs(deviationSd(p.mean, center, spread)) < NOTABLE_SD,
   }));
-  for (let i = Math.max(0, fromIndex); i < inBand.length; i++) {
-    if (!inBand[i].in) continue;
-    let run = 0;
-    for (let j = i; j < inBand.length && inBand[j].in; j++) run++;
-    if (run >= RETURN_STABILITY_DAYS) return inBand[i].day;
-  }
-  return null;
+  // Series ends out-of-band → no sustained final return (still elevated).
+  if (inBand.length === 0 || !inBand[inBand.length - 1].in) return null;
+  // Walk back from the end to the start of the final maximal in-band run.
+  let start = inBand.length - 1;
+  while (start - 1 >= 0 && inBand[start - 1].in) start--;
+  const run = inBand.length - start;
+  // The final run must be long enough AND begin at/after the first deviation.
+  if (run < RETURN_STABILITY_DAYS || start < Math.max(0, fromIndex))
+    return null;
+  return inBand[start].day;
 }
 
 /**
@@ -652,11 +743,15 @@ function firstStableReturn(
  *  - The anchor is the first logged adverse day (same role as the vital
  *    `firstDeviationIndex`): a return search starts AFTER it, so a run-up is
  *    never read as a return.
- *  - A "return" is the first logged day at/after the anchor that is in-band AND
- *    stays in-band for the next `RETURN_STABILITY_DAYS` LOGGED days. LOGGED-days
+ *  - A "return" is the START of the FINAL sustained in-band logged run at/after
+ *    the anchor — the day symptoms *finally* eased and stayed eased through the
+ *    last logged day, requiring `RETURN_STABILITY_DAYS` LOGGED days. Relapse-
+ *    aware (parity with the vital `lastStableReturn`): if symptoms ease, flare
+ *    again, then ease again, the SECOND easing is the return. LOGGED-days
  *    stability (not calendar days) is the honest-withholding handler for sparse
- *    journals: a single trailing impact-0 log never satisfies the run, so the
- *    track WITHHOLDS rather than fabricating recovery from absence of rows.
+ *    journals: a single trailing impact-0 log never satisfies the run, and a
+ *    journal that ends on an adverse log has no final in-band run, so the track
+ *    WITHHOLDS rather than fabricating recovery from absence of rows.
  *  - The gap is `dayDiff(feltBetterDay, returnedDay)`, same signed semantic.
  *  - Always `adverse:true` (a logged symptom curve is illness-relevant), so it
  *    feeds `adverseCoverageDays` and can drive the headline gap.
@@ -688,21 +783,17 @@ function computeSymptomReturn(
   const firstAdverseIndex = active.findIndex(
     (p) => p.impact >= FUNCTIONAL_IMPACT_ADVERSE_FLOOR,
   );
+  // Start of the FINAL sustained in-band logged run (relapse-aware "last
+  // return"): walk back from the last logged day. A journal ending on an
+  // adverse log has no final in-band run → null (honest withholding).
+  const inBand = active.map((p) => p.impact < FUNCTIONAL_IMPACT_ADVERSE_FLOOR);
   let returnedDay: string | null = null;
-  for (let i = firstAdverseIndex; i < active.length; i++) {
-    if (active[i].impact >= FUNCTIONAL_IMPACT_ADVERSE_FLOOR) continue;
-    // Count consecutive in-band LOGGED days from here.
-    let run = 0;
-    for (
-      let j = i;
-      j < active.length && active[j].impact < FUNCTIONAL_IMPACT_ADVERSE_FLOOR;
-      j++
-    ) {
-      run++;
-    }
-    if (run >= RETURN_STABILITY_DAYS) {
-      returnedDay = active[i].day;
-      break;
+  if (inBand.length > 0 && inBand[inBand.length - 1]) {
+    let start = inBand.length - 1;
+    while (start - 1 >= 0 && inBand[start - 1]) start--;
+    const run = inBand.length - start;
+    if (run >= RETURN_STABILITY_DAYS && start >= firstAdverseIndex) {
+      returnedDay = active[start].day;
     }
   }
 
@@ -722,6 +813,56 @@ function computeSymptomReturn(
   };
 }
 
+/**
+ * Compute the sleep-as-context observation: the user's MEDIAN asleep minutes
+ * over the well baseline vs the MEAN over the episode's active span. A neutral
+ * OBSERVATION only — never a recovery return, never folded into the gap median,
+ * never a causal claim. Mirrors the engine's withholding ethos:
+ *
+ *   - Baseline needs ≥ `SLEEP_CONTEXT_MIN_BASELINE_NIGHTS` scorable nights AND
+ *     the episode needs ≥ `SLEEP_CONTEXT_MIN_EPISODE_NIGHTS` (thin sleep data
+ *     produces no observation — say nothing rather than guess).
+ *   - The |delta| must reach `SLEEP_CONTEXT_MIN_DELTA_MINUTES` so day-to-day
+ *     jitter is never narrated as a finding.
+ *
+ * Episode nights are clipped to the active span (`>= onsetDay`) so the
+ * comparison reflects the illness, not the pre-onset lookback. Returns null
+ * (says nothing) below either floor.
+ */
+function computeSleepContext(
+  baselineNights: SleepNightPoint[],
+  episodeNights: SleepNightPoint[],
+  window: EpisodeWindow,
+): SleepContext | null {
+  const baseMinutes = baselineNights.map((n) => n.asleepMinutes);
+  const episodeMinutes = episodeNights
+    .filter((n) => n.day >= window.onsetDay)
+    .map((n) => n.asleepMinutes);
+
+  if (
+    baseMinutes.length < SLEEP_CONTEXT_MIN_BASELINE_NIGHTS ||
+    episodeMinutes.length < SLEEP_CONTEXT_MIN_EPISODE_NIGHTS
+  ) {
+    return null;
+  }
+
+  const baselineMeanMinutes = Math.round(median(baseMinutes));
+  const episodeMeanMinutes = Math.round(
+    episodeMinutes.reduce((s, v) => s + v, 0) / episodeMinutes.length,
+  );
+  const deltaMinutes = episodeMeanMinutes - baselineMeanMinutes;
+
+  // Sub-floor delta is jitter, not a finding → say nothing.
+  if (Math.abs(deltaMinutes) < SLEEP_CONTEXT_MIN_DELTA_MINUTES) return null;
+
+  return {
+    baselineMeanMinutes,
+    episodeMeanMinutes,
+    deltaMinutes,
+    nightsCounted: episodeMinutes.length,
+  };
+}
+
 /**
  * Detect the retrospective red flags — DECOUPLED from the banded loop and the
  * own-baseline band entirely. SpO2 and temperature escalate against ABSOLUTE
diff --git a/src/lib/openapi/routes/illness.ts b/src/lib/openapi/routes/illness.ts
index 4b8131e8a..66660dac0 100644
--- a/src/lib/openapi/routes/illness.ts
+++ b/src/lib/openapi/routes/illness.ts
@@ -202,6 +202,19 @@ const illnessRedFlag = z
       "A retrospective red-flag escalation (sustained low SpO2 or sustained fever) against absolute clinical floors. Copy must escalate ('seek care if this recurs'), never reassure.",
   });
 
+const illnessSleepContext = z
+  .object({
+    baselineMeanMinutes: z.number(),
+    episodeMeanMinutes: z.number(),
+    deltaMinutes: z.number(),
+    nightsCounted: z.number().int(),
+  })
+  .meta({
+    id: "IllnessSleepContext",
+    description:
+      "A neutral sleep-as-context observation: the user's median asleep minutes over the well baseline vs the mean over the episode window, and their signed delta (positive = slept more than usual). A pure OBSERVATION surfaced alongside the gap — NEVER a recovery return and NEVER part of the headline recovery-gap. Withheld (the field is null) on thin sleep data or a sub-floor delta.",
+  });
+
 const illnessCorrelationValue = z
   .object({
     episodeId: z.string(),
@@ -213,11 +226,12 @@ const illnessCorrelationValue = z
     feltBetterDay: z.string().nullable(),
     gapDriverType: z.string().nullable(),
     redFlags: z.array(illnessRedFlag),
+    sleepContext: illnessSleepContext.nullable(),
   })
   .meta({
     id: "IllnessCorrelationValue",
     description:
-      "The retrospective correlation findings for one episode: pre-onset anomaly scan, nadir, per-vital physiological returns (incl. the user-logged symptom-burden track, `type:FUNCTIONAL_IMPACT`), the headline recovery-gap (median of per-track gaps), the driving metric (`gapDriverType`), and any red flags.",
+      "The retrospective correlation findings for one episode: pre-onset anomaly scan, nadir, per-vital physiological returns (incl. the user-logged symptom-burden track, `type:FUNCTIONAL_IMPACT`), the headline recovery-gap (median of per-track gaps), the driving metric (`gapDriverType`), any red flags, and an optional sleep-as-context observation (`sleepContext`, never in the gap).",
   });
 
 const illnessCorrelationResponse = z