REM sleep occurs periodically, occupying about 25 percent of sleep time in the young adult. Episodes of REM normally recur about every 90 minutes and last 5 to 30 minutes. REM sleep is less restful than SWS and is usually associated with dreaming. Although its function is unknown, REM appears to be essential to health. Sleep was formerly attributed to decreased activity of brain systems that maintain wakefulness.
More recent data indicate that sleep, like consciousness, is an active process.
Sleep is controlled largely by nerve centers in the lower brain stem, where the base of the brain joins the spinal cord. Significantly, however, alcohol consumption affects the function of these and other chemical messengers that appear to influence sleep. Alcohol and Sleep in Those Without Alcoholism Alcohol consumed at bedtime, after an initial stimulating effect, may decrease the time required to fall asleep. Because of alcohol's sedating effect, many people with insomnia consume alcohol to promote sleep. The subject may sleep fitfully during the second half of sleep, awakening from dreams and returning to sleep with difficulty.