Typically, the symptoms of IH begin in adolescence or young adulthood, although they can begin at a later age. After onset,<unk>  often worsens over several years, but it is often stable by the time of diagnosis and appears to be a lifelong condition. Spontaneous remission is only seen in 10–15% of patients. According to the limited epidemiological data that exists, IH "has more of a female preponderance (1.8/1)." Family cases are frequent, in a range from 25% to 66% without any clear mode of inheritance." IH has long been considered a rare disease, believed to be 10 times less frequent than narcolepsy. The prevalence of narcolepsy (with cataplexy) is estimated between 1/3,300 and 1/5,000. Although the true prevalence of IH is unknown, it is estimated at 1/10,000 to 1/25,000 for the long sleep form and 1/11,000 to 1/100,000 without long sleep. A more precise estimate "is complicated by a lack of clear biologic markers" and a lack of "unambiguous diagnostic criteria." Because of the rarity of IH, research into the condition is limited "Patients are rare, researchers and scientists involved in the field are few and research findings are therefore scarce." "In Europe and in North America there is now a public health concern about helping patients and families affected by these rare diseases. Due to the complexity of the disease, they often experience difficulties to be diagnosed and often face social and professional consequences."
Idiopathic hypersomnia
Strephosymbolia
Psychoorganic syndrome
Nightmare disorder
Erotolepsy
Interictal dysphoric disorder
Narcolepsy
Klazomania