A sleep cycle lasts about 90 minutes and includes four stages: N1 (light sleep), N2 (onset), N3 (deep/slow-wave sleep), and REM (rapid eye movement / dreaming).
Stage Details
- N1 (5%): Transition from wakefulness, easily awakened
- N2 (45%): Heart rate slows, body temperature drops
- N3 (25%): Deep sleep — tissue repair, immune strengthening, growth hormone release
- REM (25%): Brain is active (dreaming), memory consolidation, emotional processing
Optimal Wake Time
Waking at the end of a full cycle (rather than mid-cycle) reduces grogginess. For 5 full cycles: 7.5 hours of sleep.