Rapid eye movement behaviour disorder, or RBD was first described in 1986 as a parasomnia involving dissociation of the characteristic stages of sleep. The major and arguably only abnormal feature of RBD is loss of muscle atonia (paralysis) during otherwise intact REM sleep (the stage of sleep in which most vivid dreaming occurs). This loss of motor inhibition leads to a wide spectrum of behavioural release during sleep. This extends from simple limb twitches to more complex integrated movements where sufferers appear to be unconsciously acting out their dreams. These behaviours are often violent in nature and commonly result in injury to either the patient or their bed partner. Injuries range from bruises and cuts to fractures, subdural hematoma and other serious injuries. In contrast, all other aspects of sleep appear similar to normal.