REM stands for Rapid Eye Movement; this is the stage of sleep that we dream. REM normally begins at or after your first 90 mins of sleep, your muscle tone is relaxed, the heart beats faster and the blood pressure increases. REM Behavior Disorder is a parasomnia. It is acting out your dreams vividly. The cause of REM Behavior Disorder is unknown. A person may swing their arms, become very physical to themselves or their bed partner and/or shout, yell, cry emotionally, and possibly laugh; however, they could make any other form of noise.