Rapid eye movement sleep behavior disorder (RBD) is a sleep disorder (more specifically a parasomnia) that involves abnormal behavior during the sleep phase with rapid eye movement (REM) sleep. It was first described in 1986. The major and arguably only abnormal feature of RBD is loss of muscle atonia (i.e., the loss of paralysis) during otherwise intact REM sleep (during which paralysis is not only normal but necessary). REM sleep is the stage of sleep in which most vivid dreaming occurs. The loss of motor inhibition leads to a wide spectrum of behavioral release during sleep. This extends from simple limb twitches to more complex integrated movement, in which sufferers appear to be unconsciously acting out their dreams. These behaviors can be violent in nature and in some cases will result in injury to either the patient or their bed partner.