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Sleep and Aging
Frequently Asked Questions
7. How many types of sleep are
there?
There are two types of sleep: non-rapid eye movement -- or NREM
sleep -- and rapid eye movement -- or REM sleep. NREM sleep has
four stages ranging from light to deep sleep. Then we go into REM
sleep, the most active stage of sleep when dreaming often occurs.
During REM sleep, the eyes move back and forth beneath the eyelids
and muscles become immobile. We cycle through these stages of
NREM-REM sleep approximately every 90 minutes.
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