REM sleep behavior disorder or RBD is a condition experienced during the REM phase of sleep in which a person acts out his dreams. Normally, during the REM phase of sleep, our brain is active similar to when we are awake but our muscles are paralyzed to prevent us from acting out our dreams. 

Unfortunately, in REM Sleep Behavior disorder, this transient muscle paralysis is lost. REM sleep behavior disorder affects 1 in 200 people with middle aged and older men being affected 10 times more commonly than women.