Other Parasomnias

As mentioned in the preceding two chapters, parasomnias may conveniently be divided into two major categories: Primary parasomnias are those due to disorders of sleep per se, and the secondary parasomnias are those that result from dysfunction of other organ systems and that take advantage of the sleeping state to declare themselves. By far, the primary sleep parasomnias are the most common; they are usually the rapid eye movement (REM) sleep behavior disorder if from REM sleep or disorders of arousal if from non-REM sleep. There remains a large group of other parasomnias, many of which are poorly understood, that can cause impressive and distressing activities arising from the sleep period but that are unrelated to disorders of arousal or REM sleep behavior disorder. This last chapter on parasomnias discusses these less-common but fascinating phenomena.