I sleep eight hours and still wake up tired

Time in bed is not the same as deep sleep, and variants in PER3 and CLOCK can compress the restorative phases so eight hours delivers far less recovery.

Why it happens

Deep sleep is when your body and brain actually repair. Some people's wiring shortens those windows, so they clock the recommended hours and still wake unrefreshed. The number on the clock looks fine, the recovery underneath it is short.

One thing to try

Keep your bedroom cooler tonight and put screens away 45 minutes before bed. Deep sleep responds to both.

Each decode is a research-backed tendency, not a diagnosis. A tap tells you how your body is likely wired and what to try, it does not label you, and nothing here is a substitute for a doctor where a medical question is involved.