- Sleep cycles last ~90 minutes.
- Waking mid-cycle causes grogginess (inertia).
- Waking between cycles feels natural and alert.
- Most adults need 5 cycles (7.5 hrs) for full recovery.
- Calculation includes 15 mins to fall asleep.
- Keep your bedroom cool (65°F / 18°C).
- Consistency beats duration—wake up at the same time.
- Avoid blue light 60 mins before bed.