11 Introduction Narcolepsy type 1 Besides excessive daytime sleepiness and cataplexy, the often referenced narcolepsy type 1 symptom pentad is completed by disturbed nocturnal sleep with frequent awakenings, hypnopompic or hypnagogic hallucinations and sleep paralysis. Many of these symptoms are hypothesized to originate from inappropriate intrusions of REM sleep phenomena while being or feeling awake, including muscle atonia during cataplexy and sleep paralysis, and the dream-like sensory fabulations of hypnagogic hallucinations [4]. Substantial weight gain close to onset of narcolepsy symptoms is regularly seen, typically starting within six months [10]. This adds to an increased prevalence in obstructive sleep apnoea compared to healthy sleepers [11]. Other nocturnal sleep disturbances are also regularly reported, including parasomnias such as REM sleep behaviour disorder, nocturnal eating disorder, and periodic limb movements [11, 12]. People with narcolepsy type 1 generally describe daytime difficulties. Excessive daytime sleepiness often leads to sleep attacks and an inability to maintain vigilance. Vigilance is vital for effective daytime functioning and people with narcolepsy consequently frequently encounter obstacles in studying or working efficiently [6, 13], and are at a higher risk of being involved in traffic accidents [14, 15]. Excessive daytime sleepiness is frequently accompanied by fatigue complaints in people with a central disorder of hypersomnolence, and results in lack of energy [16]. Narcolepsy type 1 is also associated with increased prevalence of depression and anxiety disorders. There is ongoing debate whether there is an association with attention deficit hyperactivity disorder (ADHD) or if attention problems in almost all cases can be explained by the impaired vigilance characteristic of narcolepsy. There are conflicting reports about an increased occurrence of psychotic symptoms in narcolepsy type 1 [17-21]. 1
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