You do most of your dreaming during REM sleep. But your brain paralyzes your muscles so you do not act out the dreams.
During sleep, a person usually progresses through the 3 stages of non-REM sleep before entering REM sleep. This takes about 1 to 2 hours after falling asleep. The cycle is repeated three to four times each night. An adult spends more time in NREM sleep than in REM sleep. An infant usually spends about half of the sleeping time in NREM and half in REM stages.
Dreams happen during the rapid eye movement (REM) stage of sleep. In a typical night, you dream for a total of two hours, broken up by the sleep cycle.2
Researchers do not fully understand the exact reasons why we sleep. They do know that newborns dream and that depriving rats of REM sleep greatly shortens their lives. Other mammals and birds also have REM sleep stages, but cold-blooded animals such as turtles, lizards, and fish do not.
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