REM sleep

REM sleep The portion of sleep during which rapid eye movements (REMs) occur. Dreams occur during REM sleep, and people typically have three to five periods of REM sleep per night. These periods occur at intervals of 1 to 2 hours and can vary in length from 5 minutes to over an hour. REM sleep is also characterized by rapid, low-voltage brain waves that are detectable on an electroencephalogram (EEG) recording; irregular breathing and heart rate; and involuntary muscle jerks. See also NREM sleep.