diff --git a/docs/api/openapi.yaml b/docs/api/openapi.yaml
index f5cc0e154..14d3a2fe2 100644
--- a/docs/api/openapi.yaml
+++ b/docs/api/openapi.yaml
@@ -20434,6 +20434,10 @@ components:
             type: integer
             minimum: -9007199254740991
             maximum: 9007199254740991
+        gapDriverType:
+          anyOf:
+            - type: string
+            - type: "null"
       required:
         - windowDays
         - episodeCount
@@ -20442,10 +20446,12 @@ components:
         - gapSampleSize
         - byMonth
         - byType
+        - gapDriverType
       additionalProperties: false
       description: "Cross-episode retrospective summary over the trailing window: episode + resolved counts, the typical
-        (median) recovery gap (null below the min-sample floor — withholds a thin claim), a recurrence-by-month tally,
-        and a per-type breakdown. Retrospective only."
+        (median) recovery gap (null below the min-sample floor — withholds a thin claim), a recurrence-by-month tally, a
+        per-type breakdown, and the dominant driving vital (`gapDriverType`, null when no gap is surfaced).
+        Retrospective only."
     DisclaimerAckEnvelope:
       type: object
       properties:
diff --git a/messages/de.json b/messages/de.json
index 6674ca67f..c15520593 100644
--- a/messages/de.json
+++ b/messages/de.json
@@ -6880,6 +6880,7 @@
       "countOne": "Du hast in diesem Zeitraum 1 Episode erfasst.",
       "countOther": "Du hast in diesem Zeitraum {count} Episoden erfasst.",
       "typicalGap": "Typische Erholungslücke: {days} Tage zwischen Besserung und normalisierten Werten.",
+      "typicalGapWithDriver": "Typische Erholungslücke: {days} Tage – du fühlst dich meist besser, bevor sich {vital} normalisiert.",
       "typicalGapLearning": "Noch ein paar abgeschlossene Episoden und hier erscheint eine typische Erholungslücke.",
       "none": "In diesem Zeitraum keine Episoden erfasst.",
       "analyze": "Erholungslücke analysieren"
diff --git a/messages/en.json b/messages/en.json
index 2f753c94a..4ad161b92 100644
--- a/messages/en.json
+++ b/messages/en.json
@@ -6880,6 +6880,7 @@
       "countOne": "You logged 1 episode in this period.",
       "countOther": "You logged {count} episodes in this period.",
       "typicalGap": "Typical recovery gap: {days} days between feeling better and your numbers settling.",
+      "typicalGapWithDriver": "Typical recovery gap: {days} days — you tend to feel better before your {vital} settles.",
       "typicalGapLearning": "A few more resolved episodes and a typical recovery gap will appear here.",
       "none": "No episodes logged in this period.",
       "analyze": "Analyse the recovery gap"
diff --git a/messages/es.json b/messages/es.json
index ff16bdc8f..66d9d2421 100644
--- a/messages/es.json
+++ b/messages/es.json
@@ -6880,6 +6880,7 @@
       "countOne": "Registraste 1 episodio en este período.",
       "countOther": "Registraste {count} episodios en este período.",
       "typicalGap": "Brecha de recuperación típica: {days} días entre sentirte mejor y la estabilización de tus valores.",
+      "typicalGapWithDriver": "Brecha de recuperación típica: {days} días: sueles sentirte mejor antes de que {vital} se estabilice.",
       "typicalGapLearning": "Con unos pocos episodios resueltos más aparecerá aquí una brecha de recuperación típica.",
       "none": "Sin episodios registrados en este período.",
       "analyze": "Analizar la brecha de recuperación"
diff --git a/messages/fr.json b/messages/fr.json
index a3c2c476c..608aef1a6 100644
--- a/messages/fr.json
+++ b/messages/fr.json
@@ -6880,6 +6880,7 @@
       "countOne": "Tu as enregistré 1 épisode sur cette période.",
       "countOther": "Tu as enregistré {count} épisodes sur cette période.",
       "typicalGap": "Écart de récupération typique : {days} jours entre le mieux-être et la stabilisation de tes valeurs.",
+      "typicalGapWithDriver": "Écart de récupération typique : {days} jours – tu te sens généralement mieux avant que {vital} ne se stabilise.",
       "typicalGapLearning": "Encore quelques épisodes résolus et un écart de récupération typique apparaîtra ici.",
       "none": "Aucun épisode enregistré sur cette période.",
       "analyze": "Analyser l'écart de récupération"
diff --git a/messages/it.json b/messages/it.json
index 3e512e59b..226eaebb0 100644
--- a/messages/it.json
+++ b/messages/it.json
@@ -6880,6 +6880,7 @@
       "countOne": "Hai registrato 1 episodio in questo periodo.",
       "countOther": "Hai registrato {count} episodi in questo periodo.",
       "typicalGap": "Divario di recupero tipico: {days} giorni tra il sentirti meglio e la stabilizzazione dei valori.",
+      "typicalGapWithDriver": "Divario di recupero tipico: {days} giorni: di solito ti senti meglio prima che {vital} si stabilizzi.",
       "typicalGapLearning": "Ancora qualche episodio risolto e qui apparirà un divario di recupero tipico.",
       "none": "Nessun episodio registrato in questo periodo.",
       "analyze": "Analizza il divario di recupero"
diff --git a/messages/pl.json b/messages/pl.json
index 9709e45af..4853b2972 100644
--- a/messages/pl.json
+++ b/messages/pl.json
@@ -6880,6 +6880,7 @@
       "countOne": "W tym okresie zapisałeś 1 epizod.",
       "countOther": "W tym okresie zapisałeś {count} epizodów.",
       "typicalGap": "Typowa luka rekonwalescencji: {days} dni między poprawą a ustabilizowaniem wartości.",
+      "typicalGapWithDriver": "Typowa luka rekonwalescencji: {days} dni – zwykle czujesz się lepiej, zanim {vital} się ustabilizuje.",
       "typicalGapLearning": "Jeszcze kilka zakończonych epizodów i pojawi się tu typowa luka rekonwalescencji.",
       "none": "Brak epizodów zapisanych w tym okresie.",
       "analyze": "Przeanalizuj lukę rekonwalescencji"
diff --git a/src/app/api/illness/insights/route.ts b/src/app/api/illness/insights/route.ts
index f11ec4bab..0e31fb6d3 100644
--- a/src/app/api/illness/insights/route.ts
+++ b/src/app/api/illness/insights/route.ts
@@ -85,7 +85,11 @@ export const GET = apiHandler(async (request: NextRequest) => {
   // out of the typical-gap median by the aggregate's signal-density gates.
   const gapById = new Map<
     string,
-    { recoveryGapDays: number | null; gapMeasurementDays: number }
+    {
+      recoveryGapDays: number | null;
+      gapMeasurementDays: number;
+      gapReturnTypes: string[];
+    }
   >();
   if (includeRecoveryGap) {
     const gapCandidates = rows
@@ -98,7 +102,11 @@ export const GET = apiHandler(async (request: NextRequest) => {
           async (): Promise<
             [
               string,
-              { recoveryGapDays: number | null; gapMeasurementDays: number },
+              {
+                recoveryGapDays: number | null;
+                gapMeasurementDays: number;
+                gapReturnTypes: string[];
+              },
             ]
           > => {
             const derived = await computeEpisodeCorrelation(
@@ -130,6 +138,15 @@ export const GET = apiHandler(async (request: NextRequest) => {
                   derived.status === "ok"
                     ? derived.value.adverseCoverageDays
                     : 0,
+                // The vitals that produced a real physiological return —
+                // tallied across the qualifying episodes to name the dominant
+                // driving vital in the summary copy.
+                gapReturnTypes:
+                  derived.status === "ok"
+                    ? derived.value.returns
+                        .filter((r) => r.gapDays !== null)
+                        .map((r) => String(r.type))
+                    : [],
               },
             ];
           },
@@ -148,6 +165,7 @@ export const GET = apiHandler(async (request: NextRequest) => {
       resolved: r.resolvedAt !== null,
       recoveryGapDays: gap?.recoveryGapDays ?? null,
       gapMeasurementDays: gap?.gapMeasurementDays ?? 0,
+      gapReturnTypes: gap?.gapReturnTypes ?? [],
       lifecycle: r.lifecycle,
     };
   });
@@ -160,6 +178,7 @@ export const GET = apiHandler(async (request: NextRequest) => {
       episode_count: summary.episodeCount,
       gap_sample_size: summary.gapSampleSize,
       typical_gap_days: summary.typicalRecoveryGapDays,
+      gap_driver_type: summary.gapDriverType,
       include_recovery_gap: includeRecoveryGap,
     },
   });
diff --git a/src/components/illness/illness-insights-card.tsx b/src/components/illness/illness-insights-card.tsx
index 15ea9f02f..86beede7a 100644
--- a/src/components/illness/illness-insights-card.tsx
+++ b/src/components/illness/illness-insights-card.tsx
@@ -87,13 +87,22 @@ export function IllnessInsightsCard({
               <p className="text-muted-foreground">
                 {t("illness.insights.typicalGapLearning")}
               </p>
+            ) : gap.data.typicalRecoveryGapDays === null ? (
+              <p className="text-muted-foreground">
+                {t("illness.insights.typicalGapLearning")}
+              </p>
+            ) : gap.data.gapDriverType ? (
+              <p className="text-muted-foreground">
+                {t("illness.insights.typicalGapWithDriver", {
+                  days: gap.data.typicalRecoveryGapDays,
+                  vital: t(`illness.vital.${gap.data.gapDriverType}`),
+                })}
+              </p>
             ) : (
               <p className="text-muted-foreground">
-                {gap.data.typicalRecoveryGapDays !== null
-                  ? t("illness.insights.typicalGap", {
-                      days: gap.data.typicalRecoveryGapDays,
-                    })
-                  : t("illness.insights.typicalGapLearning")}
+                {t("illness.insights.typicalGap", {
+                  days: gap.data.typicalRecoveryGapDays,
+                })}
               </p>
             )}
           </div>
diff --git a/src/components/illness/types.ts b/src/components/illness/types.ts
index ec3563e1b..6bda26316 100644
--- a/src/components/illness/types.ts
+++ b/src/components/illness/types.ts
@@ -149,4 +149,5 @@ export interface IllnessInsightsResponse {
   gapSampleSize: number;
   byMonth: Record<string, number>;
   byType: Record<string, number>;
+  gapDriverType: string | null;
 }
diff --git a/src/lib/illness/__tests__/retrospective.test.ts b/src/lib/illness/__tests__/retrospective.test.ts
index 878072f52..f9dc38125 100644
--- a/src/lib/illness/__tests__/retrospective.test.ts
+++ b/src/lib/illness/__tests__/retrospective.test.ts
@@ -131,6 +131,74 @@ describe("summarizeIllnessRetrospective", () => {
     expect(out.typicalRecoveryGapDays).toBeNull(); // …but the magnitude is noise
   });
 
+  it("names the dominant driving vital when a gap is surfaced", () => {
+    const out = summarizeIllnessRetrospective([
+      ep({
+        id: "a",
+        recoveryGapDays: 4,
+        gapReturnTypes: ["RESTING_HEART_RATE"],
+      }),
+      ep({
+        id: "b",
+        recoveryGapDays: 6,
+        gapReturnTypes: ["RESTING_HEART_RATE", "HEART_RATE_VARIABILITY"],
+      }),
+      ep({
+        id: "c",
+        recoveryGapDays: 5,
+        gapReturnTypes: ["HEART_RATE_VARIABILITY"],
+      }),
+    ]);
+    // RHR returned in 2 of 3 episodes, HRV in 2 as well — tie → deterministic
+    // alphabetical resolution picks HEART_RATE_VARIABILITY.
+    expect(out.typicalRecoveryGapDays).toBe(5);
+    expect(out.gapDriverType).toBe("HEART_RATE_VARIABILITY");
+  });
+
+  it("picks the strictly-most-frequent driver", () => {
+    const out = summarizeIllnessRetrospective([
+      ep({
+        id: "a",
+        recoveryGapDays: 4,
+        gapReturnTypes: ["RESTING_HEART_RATE"],
+      }),
+      ep({
+        id: "b",
+        recoveryGapDays: 6,
+        gapReturnTypes: ["RESTING_HEART_RATE"],
+      }),
+      ep({
+        id: "c",
+        recoveryGapDays: 5,
+        gapReturnTypes: ["HEART_RATE_VARIABILITY"],
+      }),
+    ]);
+    expect(out.gapDriverType).toBe("RESTING_HEART_RATE");
+  });
+
+  it("leaves the driver null when no gap is surfaced", () => {
+    const out = summarizeIllnessRetrospective([
+      ep({
+        id: "a",
+        recoveryGapDays: 0,
+        gapReturnTypes: ["RESTING_HEART_RATE"],
+      }),
+      ep({
+        id: "b",
+        recoveryGapDays: 1,
+        gapReturnTypes: ["RESTING_HEART_RATE"],
+      }),
+      ep({
+        id: "c",
+        recoveryGapDays: -1,
+        gapReturnTypes: ["RESTING_HEART_RATE"],
+      }),
+    ]);
+    // Magnitude gate withholds the gap → no driver is named.
+    expect(out.typicalRecoveryGapDays).toBeNull();
+    expect(out.gapDriverType).toBeNull();
+  });
+
   it("surfaces a negative gap once its magnitude clears the floor", () => {
     const out = summarizeIllnessRetrospective([
       ep({ id: "a", recoveryGapDays: -2 }),
diff --git a/src/lib/illness/retrospective.ts b/src/lib/illness/retrospective.ts
index ff93e92b0..8e01c45c4 100644
--- a/src/lib/illness/retrospective.ts
+++ b/src/lib/illness/retrospective.ts
@@ -62,6 +62,14 @@ export interface RetrospectiveEpisode {
    * the engine computed one. Absent/0 → does not qualify.
    */
   gapMeasurementDays?: number;
+  /**
+   * The vital metric types that produced a non-null physiological-return gap
+   * for this episode (the engine's `returns[]` filtered to a real return).
+   * Tallied across the qualifying episodes to name the dominant driving vital
+   * in the cross-episode summary ("felt better ~X days before resting heart
+   * rate settled"). Absent/empty → contributes no driver.
+   */
+  gapReturnTypes?: string[];
   /** Lifecycle — CHRONIC_ONGOING never contributes a gap. */
   lifecycle: string;
 }
@@ -87,6 +95,13 @@ export interface IllnessRetrospectiveSummary {
   byMonth: Record<number, number>;
   /** Per-type episode counts in the window (retrospective breakdown). */
   byType: Record<string, number>;
+  /**
+   * The dominant vital that drove the typical recovery gap — the metric type
+   * that most often produced a physiological return across the qualifying
+   * episodes — or null when no gap is surfaced or no vital clearly leads. The
+   * card names it ("…before resting heart rate settled"). Retrospective only.
+   */
+  gapDriverType: string | null;
 }
 
 /**
@@ -109,6 +124,10 @@ export function summarizeIllnessRetrospective(
   const byType: Record<string, number> = {};
   let resolvedCount = 0;
   const gaps: number[] = [];
+  // Tally of which vital produced a physiological return, across only the
+  // episodes that qualified for the typical-gap median — the dominant one
+  // names the driving vital in the card.
+  const driverTally: Record<string, number> = {};
 
   for (const e of episodes) {
     const month = Number(e.onsetDay.slice(5, 7));
@@ -124,6 +143,8 @@ export function summarizeIllnessRetrospective(
       (e.gapMeasurementDays ?? 0) >= MIN_GAP_MEASUREMENT_DAYS
     ) {
       gaps.push(e.recoveryGapDays);
+      for (const type of e.gapReturnTypes ?? [])
+        driverTally[type] = (driverTally[type] ?? 0) + 1;
     }
   }
 
@@ -139,6 +160,16 @@ export function summarizeIllnessRetrospective(
       ? medianGap
       : null;
 
+  // Name the driving vital only when a gap is actually surfaced — the most
+  // frequently-returning vital across the qualifying episodes. Ties resolve
+  // deterministically by metric name so the copy is stable across reads.
+  const gapDriverType =
+    typicalRecoveryGapDays !== null
+      ? (Object.entries(driverTally).sort((a, b) =>
+          b[1] !== a[1] ? b[1] - a[1] : a[0] < b[0] ? -1 : 1,
+        )[0]?.[0] ?? null)
+      : null;
+
   return {
     episodeCount: episodes.length,
     resolvedCount,
@@ -146,5 +177,6 @@ export function summarizeIllnessRetrospective(
     gapSampleSize: gaps.length,
     byMonth,
     byType,
+    gapDriverType,
   };
 }
diff --git a/src/lib/openapi/routes/illness.ts b/src/lib/openapi/routes/illness.ts
index 2c8bc9571..900f49119 100644
--- a/src/lib/openapi/routes/illness.ts
+++ b/src/lib/openapi/routes/illness.ts
@@ -253,11 +253,12 @@ const illnessInsightsResponse = z
     gapSampleSize: z.number().int(),
     byMonth: z.record(z.string(), z.number().int()),
     byType: z.record(z.string(), z.number().int()),
+    gapDriverType: z.string().nullable(),
   })
   .meta({
     id: "IllnessInsightsResponse",
     description:
-      "Cross-episode retrospective summary over the trailing window: episode + resolved counts, the typical (median) recovery gap (null below the min-sample floor — withholds a thin claim), a recurrence-by-month tally, and a per-type breakdown. Retrospective only.",
+      "Cross-episode retrospective summary over the trailing window: episode + resolved counts, the typical (median) recovery gap (null below the min-sample floor — withholds a thin claim), a recurrence-by-month tally, a per-type breakdown, and the dominant driving vital (`gapDriverType`, null when no gap is surfaced). Retrospective only.",
   });
 
 const episodeNotFound = {