Sleep overview

• Sleep is entered through NREM sleep.
• Sleep cycles of 90 minutes, 4-6 cycles per night sleep.
• Non-REM 3 predominates in the first third of the night and is linked to the initiation of sleep.
• REM sleep predominates in the last third of the night

• Wakefulness in sleep usually accounts for less than 5% of the night.
• Non-REM 1 sleep approximately 2% to 5% of sleep.
• Non-REM 2 sleep approximately 45% to 55% of sleep.
• Non-REM 3 sleep approximately 15% to 20% of sleep.
• Non REM sleep, therefore, is usually 75% to 80% of sleep.
• REM sleep is usually 20% to 25% of sleep, occurring in four to six episodes.

Sleep stadium	Sleep pattern
Non-REM 1	Slow rolling eye movements (SREMs), decrease of alpha rhythm, POSTS (Positive occipital sharp transients of sleep), Vertex waves
Non-REM 2	Sleep spindles, K complex, <20% Delta waves
Non-REM 3	>20% Delta waves
REM sleep	Low voltage background, rapid eye movements, muscle atonia