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↓ why this works

You woke up naturally, felt surprisingly clear, then went back to sleep. You woke to your alarm feeling wrecked.

That wasn't extra rest: that was sleep inertia. You fell back into a deep sleep stage your brain wasn't ready to leave.

Sleep runs in 90-minute cycles. Each ends in a brief window of near-wakefulness before the next begins. Early cycles are heavy on deep slow-wave sleep: restorative, physically intense, brutal to wake from. Later cycles shift toward REM and lighter sleep.

Waking between cycles, not inside one, is the difference. Rhythm calculates exactly those windows.

sleep cycle calculator · why do i feel worse after more sleep · sleep inertia · 90 minute sleep cycles · best time to wake up · circadian rhythm · REM sleep · deep sleep stages · how to wake up feeling refreshed

Times already account for the ~14 min it takes to fall asleep. Get into bed at the shown time.