During sleep, the body cycles between non-REM and REM
sleep. Typically, people begin the
sleep cycle with a period of non-REM
sleep followed by a very short period of REM sleep. Dreams generally occur in the REM stage of sleep.
Intense dreaming occurs during REM sleep as a result of heightened brain activity, but paralysis occurs simultaneously in the major voluntary muscle groups. REM is a mixture of encephalic (brain) states of excitement and muscular immobility.