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Sleep is divided into “light sleep” and “deep sleep”

The drawing above records what stage of sleep we are in, over time, for a full night. It’s called a “hypnogram” . In “light sleep” we are not paralyzed we are not making new memories and we are not fully conscious. In “deep sleep” we get paralyzed and we are doing the “work” of sleep.

Here’s how to read the hypnogram: Start on the left with light sleep at 10:00pm. Then at about 10:30p comes the first stage of deep slow sleep, or Slow Wave Sleep (SWS).  We do deep sleep in blocks of time, usually no more than an hour, because we’re paralyzed in deep sleep. Then we switch to light sleep, (not paralyzed) change position, and go back into deep sleep again. We do more SWS at the beginning of the night and more REM sleep toward the end of the night. Most of the REM sleep happens between 3-6 am. Usually if you wake in a dream you were in REM sleep. Deep Sleep is either SWS or REM sleep. REM = Rapid Eye Movement.