Behavioral parasomnias.

Sleep is not a static state. During the sleep period, physiologic changes occur throughout the body and brain. This complex, dynamic process can, at times, result in episodes of unusual or undesirable behaviors. These phenomena are called parasomnias. The accurate diagnosis of this group of treatable disorders is important, because they can have a negative impact on sleep, health, and social function. In addition, some of the parasomnias may provide clues to the presence of other underlying pathologic conditions. The parasomnias may be categorized in more than one way, but any attempt to classify such a diverse collection of entities is likely to be somewhat arbitrary. This article discusses the parasomnias according to the classification of the International Classification of Sleep Disorders, with emphasis on those characterized by observable behavior. As the understanding of these disorders (and sleep, in general) continues to deepen, new entities and schemes of classification may emerge.