Stages of Sleep

People usually cycle through different stages of sleep throughout the night.  Time spent in these stages may vary with age.

Non-REM (70-80% of sleep) – As you fall asleep, you enter non-REM sleep, which consists of Stages 1-4.
Stage 1 – Drowsiness and light sleep.
Stage 2 – This stage takes up a majority of a night’s total sleep.  It is defined by unique EEG characteristics.
Stages 3 & 4 – Deepest and most restorative sleep:  blood pressure drops, breathing slows down and hormones are released for growth and development in youths.

REM (20-30% of sleep) – Occurs in episodes beginning about 90 minutes after the onset of sleep and recurring with lengthening episodes about every 90 minutes.  Most REM sleep is during the latter half of the night.  The brain is active and dreams occur as the eyes dart back and forth.  The body becomes relaxed and immobile. Breathing and heart rate may become irregular.  A person with obstructive sleep apnea may have difficulty reaching REM sleep.