diff --git a/messages/de.json b/messages/de.json
index 3dcc80763..4e8cd7244 100644
--- a/messages/de.json
+++ b/messages/de.json
@@ -2547,7 +2547,8 @@
         "asleepTotal": "Geschlafen {value}",
         "inBedTotal": "Im Bett {value}",
         "awakenings": "{count} Wachphasen",
-        "source": "Quelle: {source}"
+        "source": "Quelle: {source}",
+        "estimateNote": "Die Phasen-Zeiten sind geschätzt — diese Quelle liefert Summen je Phase, keinen gemessenen Verlauf."
       },
       "stages": {
         "deep": "Tief",
diff --git a/messages/en.json b/messages/en.json
index a87949920..5c4c0206d 100644
--- a/messages/en.json
+++ b/messages/en.json
@@ -2547,7 +2547,8 @@
         "asleepTotal": "Asleep {value}",
         "inBedTotal": "In bed {value}",
         "awakenings": "{count} awakenings",
-        "source": "Source: {source}"
+        "source": "Source: {source}",
+        "estimateNote": "Stage timing is estimated — this source reports totals per stage, not a measured timeline."
       },
       "stages": {
         "deep": "Deep",
diff --git a/messages/es.json b/messages/es.json
index 99b6d7782..a69ad908c 100644
--- a/messages/es.json
+++ b/messages/es.json
@@ -2547,7 +2547,8 @@
         "asleepTotal": "Dormido {value}",
         "inBedTotal": "En la cama {value}",
         "awakenings": "{count} despertares",
-        "source": "Fuente: {source}"
+        "source": "Fuente: {source}",
+        "estimateNote": "Los tiempos de cada fase son estimados: esta fuente informa totales por fase, no una cronología medida."
       },
       "stages": {
         "deep": "Profundo",
diff --git a/messages/fr.json b/messages/fr.json
index 85cb525e9..8ca52cec5 100644
--- a/messages/fr.json
+++ b/messages/fr.json
@@ -2547,7 +2547,8 @@
         "asleepTotal": "Sommeil {value}",
         "inBedTotal": "Au lit {value}",
         "awakenings": "{count} réveils",
-        "source": "Source : {source}"
+        "source": "Source : {source}",
+        "estimateNote": "Les durées des phases sont estimées : cette source indique des totaux par phase, pas une chronologie mesurée."
       },
       "stages": {
         "deep": "Profond",
diff --git a/messages/it.json b/messages/it.json
index 48507ed1d..7608d2186 100644
--- a/messages/it.json
+++ b/messages/it.json
@@ -2547,7 +2547,8 @@
         "asleepTotal": "Sonno {value}",
         "inBedTotal": "A letto {value}",
         "awakenings": "{count} risvegli",
-        "source": "Fonte: {source}"
+        "source": "Fonte: {source}",
+        "estimateNote": "I tempi delle fasi sono stimati: questa sorgente riporta i totali per fase, non una cronologia misurata."
       },
       "stages": {
         "deep": "Profondo",
diff --git a/messages/pl.json b/messages/pl.json
index c60c651f4..32e690173 100644
--- a/messages/pl.json
+++ b/messages/pl.json
@@ -2547,7 +2547,8 @@
         "asleepTotal": "Sen {value}",
         "inBedTotal": "W łóżku {value}",
         "awakenings": "{count} przebudzeń",
-        "source": "Źródło: {source}"
+        "source": "Źródło: {source}",
+        "estimateNote": "Czasy faz są szacowane — to źródło podaje sumy dla każdej fazy, a nie zmierzony przebieg."
       },
       "stages": {
         "deep": "Głęboki",
diff --git a/src/components/insights/__tests__/sleep-hypnogram.test.tsx b/src/components/insights/__tests__/sleep-hypnogram.test.tsx
index a04a0ea17..6452cd205 100644
--- a/src/components/insights/__tests__/sleep-hypnogram.test.tsx
+++ b/src/components/insights/__tests__/sleep-hypnogram.test.tsx
@@ -127,6 +127,30 @@ describe("<SleepHypnogram> — timeline bar visibility", () => {
     expect(render(session)).toContain('role="img"');
   });
 
+  it("suppresses the timeline bar for a SYNTHESISED (reconstructed) night", () => {
+    // WHOOP / Polar report per-stage TOTALS and the server lays the segments
+    // out in a fixed physiological order — the timeline would invent a phase
+    // progression that was never measured. So even with distinct, well-timed
+    // spans, a `reconstructed` night drops the bar and keeps the breakdown.
+    const session: SleepHypnogramSession = {
+      ...baseSession,
+      source: "WHOOP",
+      reconstructed: true,
+    };
+    const html = render(session);
+    expect(html).not.toContain('role="img"');
+    expect(html).toContain('data-slot="sleep-hypnogram-breakdown"');
+    expect(html).toContain('data-slot="sleep-hypnogram-estimate-note"');
+  });
+
+  it("keeps the timeline bar for a measured (non-reconstructed) night", () => {
+    // An Apple Health night carries real per-stage onsets, so the stepped bar
+    // is genuine and stays. The estimate note never appears.
+    const html = render({ ...baseSession, reconstructed: false });
+    expect(html).toContain('role="img"');
+    expect(html).not.toContain('data-slot="sleep-hypnogram-estimate-note"');
+  });
+
   it("collapses to the breakdown footer for a degenerate single-instant session", () => {
     // Every segment stamped on ONE instant — no real timeline, so only the
     // breakdown footer, no bar.
diff --git a/src/components/insights/sleep-hypnogram.tsx b/src/components/insights/sleep-hypnogram.tsx
index 27b341252..7e6797140 100644
--- a/src/components/insights/sleep-hypnogram.tsx
+++ b/src/components/insights/sleep-hypnogram.tsx
@@ -58,6 +58,17 @@ export interface SleepHypnogramSession {
   awakenings: number;
   stages: Record<string, number>;
   segments: SleepHypnogramSegment[];
+  /**
+   * `true` when the winning source has no measured per-stage onset
+   * timestamps and the server synthesised a contiguous timeline in a fixed
+   * physiological order (WHOOP / Polar). The "timeline" of such a night is
+   * not a real hypnogram — it would read as one long Core block followed by
+   * one Deep block, never the phase-to-phase progression a measured night
+   * shows — so we never draw the misleading stepped bar for it and fall back
+   * to the per-stage breakdown alone. A real-series source (Apple Health,
+   * Withings, Fitbit) is `false` and keeps the timeline.
+   */
+  reconstructed?: boolean;
 }
 
 export interface SleepHypnogramProps {
@@ -216,10 +227,16 @@ export function SleepHypnogram({ session }: SleepHypnogramProps) {
   // breakdown footer. (Gating on the END instant instead hid the bar for an
   // ordinary multi-stage night whose segments happened to share a right
   // edge — the regression this restores.)
+  // A SYNTHESISED night (WHOOP / Polar) has no measured stage onsets — the
+  // server laid its segments out in a fixed physiological order, so drawing
+  // the stepped bar would invent a phase progression that was never recorded
+  // (the "Core block then Deep block, no real breakdown" the bar reads as).
+  // For those we keep the per-stage breakdown + totals, which ARE real, and
+  // drop the misleading timeline entirely. Real-series sources keep the bar.
   const hasTrack =
+    session.reconstructed !== true &&
     spans.length > 0 &&
-    (spans.length === 1 ||
-      new Set(spans.map((s) => s.x1)).size > 1);
+    (spans.length === 1 || new Set(spans.map((s) => s.x1)).size > 1);
   const hasBreakdown = breakdown.length > 0;
 
   return (
@@ -251,6 +268,18 @@ export function SleepHypnogram({ session }: SleepHypnogramProps) {
               })}
             </span>
           ) : null}
+          {/* When the source reports stage TOTALS but no measured onsets
+              (WHOOP / Polar) the stepped timeline is suppressed — drawing one
+              would invent a phase order that was never recorded. Surface a calm
+              note so the breakdown below doesn't read as a missing chart. */}
+          {session.reconstructed === true && hasBreakdown ? (
+            <span
+              data-slot="sleep-hypnogram-estimate-note"
+              className="text-muted-foreground/70 text-xs"
+            >
+              {t("insights.sleep.hypnogram.estimateNote")}
+            </span>
+          ) : null}
         </div>
       </CardHeader>
       <CardContent className="space-y-3">