Narcolepsy is best characterized as a disorder of the regulation of sleep and wakefulness, resulting in a variety of symptoms such as excessive daytime sleepiness (EDS), cataplexy, hypnagogic hallucinations (HH), sleep paralysis, and disturbed nocturnal sleep. This chapter focuses on narcolepsy with cataplexy and narcolepsy without cataplexy. Cataplexy is characterized by a sudden bilateral loss of muscle tone, with preserved consciousness, elicited by emotions. Narcolepsy with cataplexy is diagnosed according to the criteria of the International Classification of Sleep Disorders (ICSD-2). The chapter summarizes the differential diagnoses of EDS and cataplexy. Cataplexy and sleep paralysis are both regarded as expressions of the atonia that physiologically occurs during REM sleep, occurring during wakefulness. Two treatment modalities have proven to be effective: behavioral modification and pharmacological therapy. Pharmacological treatment is supplementary to behavioral advice and should be tailored individually.

Hallucinations occur when sensations are perceived in the absence of environmental stimuli. They are generated by the brain under normal or abnormal situations, including drowsiness, sensory deprivation, use of or withdrawal from drugs or toxins, structural or metabolic brain disease, seizures or migraine, and psychiatric disorders such as schizophrenia. Hypnagogic and hypnopompic hallucinations (HH) are typically visual, but can be auditory, tactile or kinetic. Complex nocturnal visual hallucinations (CNVH) have somewhat different phenomenology and putative pathophysiology from HHs and can be seen in a variety of pathologic conditions. CNVH have similar phenomenology and represent a final common pathway for a variety of etiologies. The exploding head syndrome (EHS) is thought to be a benign condition characterized by an imagined very loud sound or explosion in the head at sleep onset or on waking during night.