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Sleep and Aging
About Sleep
There are two types of sleep: non-rapid eye movement -- or NREM
sleep -- and rapid eye movement -- or REM sleep. NREM sleep
includes four stages, ranging from light to deep sleep. We cycle
through these four stages of sleep approximately every 90 minutes.
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.
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