What happens when I sleep?
You don't notice it, of course, but while you're asleep,
your brain is still active. As people sleep, their brains
pass through five stages of sleep. Together, these stages —
which doctors call 1, 2, 3, 4 and REM (rapid eye
movement) sleep — make up a sleep cycle. One complete
sleep cycle lasts about 90 to 100 minutes. So during an
average night's sleep, a person will experience about four
or five cycles of sleep.
Stages 1 and 2 are periods of light sleep from which a
person can easily be awakened. During these stages, eye
movements slow down and eventually stop, heart and
breathing rates slow down and body temperature
decreases. Stages 3 and 4 are deep sleep stages. It's more
difficult to awaken someone during these stages, and
when awakened, a person will often feel groggy and
disoriented for a few minutes. Stages 3 and 4 are the
most refreshing of the sleep stages — it is this type of
sleep that we crave when we are very tired.
The final stage of the sleep cycle is known as REM
sleep because of the rapid eye movements that
occur during this stage. During REM sleep,
other physical changes take place —
breathing becomes rapid, the heart beats
faster and the limb muscles
don't move. This is the stage of
sleep when a person has the
most vivid dreams.
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