Overview of Sleep
Many people think of sleep as a passive activity, but sleep is actually an active
state. It restores us, helps the body to repair damage and grow new cells, keeps the
body's nervous system working properly, and helps us to consolidate memory (helps us to
remember what we learned during the day). During sleep, a person passes through 5 phases,
or stages, of sleep - stages 1, 2, 3, 4 of quiet sleep and stage 5, called REM (rapid eye
Stage 1 sleep is light sleep, where we drift in and out of sleep and can
be woken up easily. Eyes move very slowly and muscle activity slows down.
A person spends almost half of their total sleep time in Stage 2 sleep.
Eye movements stop and brain waves (or activity) become slower.
Stages 3 and 4 are called deep sleep. During Stage 3 sleep, brain waves
slow down even more and the brain makes mostly delta waves (slow brain waves).
The brain makes only delta waves during Stage 4 sleep and there is no eye movement or
muscle activity. People often feel groggy and disoriented for a few minutes when they are
woken up during deep sleep. Some children have bedwetting, night terrors, or sleepwalking
during deep sleep. Deep sleep restores us, helping to grow new cells and repair cells from
A person's breathing becomes more rapid, irregular, and shallow in REM
sleep. The eyes jerk quickly in many directions, heart rate increases, and blood pressure
rises. When people wake up during REM sleep, they often describe strange dreams that don't
make any sense. Most dreaming happens during REM sleep. REM sleep is important, perhaps in
part because it stimulates the parts of the brain that help us learn.
A person cycles through these 5 stages of sleep during the night. The first sleep
cycles contain short REM periods and long periods of deep sleep. REM sleep periods become
longer in length while deep sleep decreases. By morning, almost all sleep time is in
stages 1, 2, and REM.
Sleep Disorders Overview
Overview of Sleep
Amount of Sleep Needed
Diagnosis of Sleep Disorders
Prevention of Sleep Disorders