Parasomnias

Abstract Parasomnias are sleep disorders that involve abnormal actions or experiences during sleep, often due to dissociated states in which there is a simultaneous coexistence of sleep and wake. Parasomnias are divided into two categories: those that occur during nonrapid eye movement sleep (NREM) and those occurring during rapid eye movement sleep (REM). NREM parasomnias include sleepwalking and night terrors. Examples of REM parasomnias are nightmares, hypnogogic hallucinations, and REM behavior disorder. Although many parasomnias in themselves are considered benign, they are clinically relevant as some have been shown to be associated with psychiatric illness (e.g., nightmare disorder) and neurodegenerative diseases (e.g., REM behavior disorder).