1. The sleep staircase
Sleep does not progress through these stages in sequence.
( – )
Sleep begins in stage 1 and goes into stages 2, 3 & 4.

2. The sleep staircase
After stage 4 sleep, stage 3 & then stage 2 sleep are repeated before entering REM sleep.
( REM – REM)
Once REM sleep is over, we usually return to stage 2 sleep.
We go through these sleep cycles four or five times a night.

5. REM gets longer
On average, we enter the REM stage about 90 minutes after falling asleep.
The 1st REM cycle might last a short amount of time, but each cycle becomes longer. So we dream more toward morning.

6. Normal Sleep Architecture
Entered through NREM
Approximately 90 minute cycle including NREM and REM
Slow wave dominates first third of night
REM sleep dominates last third of night
REM sleep: 20-25% total sleep time

7. Clips
Stages of sleep Sleep cycles (8 mins 46)

8. Activity