GUIDE深度 · Deep dive
What Are Sleep Cycles?
Sleep cycles through N1, N2, N3 and REM about four to six times a night, roughly 90 minutes each. Deep sleep and REM are distributed differently across the night, so eight hours does not automatically mean good sleep.
Four stages
N1 is the light transition, N2 is the largest share, N3 is deep sleep and REM supports dreaming and memory.
Cycle length varies by person; 90 minutes is only an average.
Why you wake up groggy
Waking during deep sleep causes sleep inertia; waking near the end of a cycle is often easier.
An alarm can roughly align with cycles but cannot replace a regular schedule.
FAQ
Do I need five full cycles?
No; total duration and daytime function matter more; cycles are a guide.
Does alcohol help sleep?
It may shorten time to sleep but disrupts REM and deep sleep later, reducing quality.