Normal sleep has two states; non-rapid eye movement and rapid eye movement (REM) sleep, which last about three-quarters of the night and one-quarter of the night, respectively. During normal REM sleep, the eyes move rapidly, breathing becomes irregular, blood pressure rises, and muscles lose tone in a type of temporary protective natural paralysis. The sleeper usually dreams during REM and the brain is often as active as when awake.
In REM sleep-behavior disorder (RBD), natural muscle paralysis does not occur, allowing the person to physically “act out” his or her vivid and intense dreams. Eight men with RBD took 3 mg of melatonin each night between 10:00 p.m. and 11:00 p.m., or a placebo. After four weeks, while the placebo group had not improved, men who had taken melatonin had 30 percent fewer REM sleep periods without paralysis, and healthier REM sleep continued for four weeks after the men stopped taking melatonin.