Narcolepsy
affects less than 0.05% of the population, and is most commonly diagnosed
during adolescence and early adulthood. Diagnostically, narcolepsy is divided
into two subtypes. Narcolepsy type 1 (NT1) is
characterized by the presence of orexin deficiency and cataplexy, and the pathophysiology in NT1 involves the
partial or complete cessation of orexin production by neurons in the lateral
hypothalamus. Narcolepsy type 2 (NT2) presents without
cataplexy and orexin levels are normal or only slightly reduced. The pathophysiological mechanism is
thus less clear in NT2. The main symptoms of narcolepsy are excessive daytime
sleepiness (EDS) which culminates in involuntary lapses into sleep during
daytime, and disrupted nocturnal sleep. These symptoms are often more severe in
NT1 than NT2 patients. In addition to sleep-wake regulation problems,
unpleasant phenomena during nocturnal sleep and daytime naps and sleep attacks
are common in narcolepsy patients. Dreams of narcolepsy patients are typically
rated to be more vivid, bizarre and emotional, and they report recalling dreams
and nightmares more often than healthy controls. Other unpleasant experiences,
such as Non-Rapid Eye Movement (NREM) and Rapid Eye Movement (REM) sleep
parasomnia symptoms, including sleep walking, sleep terrors and REM Sleep
Behaviour Disorder (RBD), are also more prevalent in narcolepsy patients than
in general population. Undesirable phenomena during sleep are often accompanied
by equally distressing sleep-wake transition experiences. Sleep paralysis
episodes are more common in narcolepsy patients than in healthy individuals and
frequently accompanied by frightening hypnagogic or hypnopompic hallucinations,
occurring at the onset or offset of sleep, respectively. The waking lives of
narcolepsy patients are affected in many ways by their sleep-related
experiences. Many patients with narcolepsy experience confusion of memory
sources, and may hold delusional beliefs, sometimes for extended periods of
time, that a memory created by a dream is a memory of a real experience.
Nightmares, parasomnias, sleep paralysis and hypnagocic and hypnopompic
hallucinations, as well as the inability to distinguish dream memories from
waking memories, can be highly distressing for the patients. Narcolepsy
patients also have a higher prevalence of psychiatric symptoms, especially
depression and anxiety. The illness usually has significant effects on the
patients’ daily lives, functional abilities and life courses. Therefore, awareness
of narcolepsy and its associated symptoms, and efficient treatment of not only
daytime sleepiness but sleep-related distressing symptoms, might increase the
psychological well-being and quality of life of the patients.