Idiopathic hypersomnia is a 24-hour disorder.

Idiopathic hypersomnia is a heterogeneous disorder with daytime and nighttime symptoms that have a profound 24-hour effect on individuals' well-being. Daytime signs and symptoms include excessive daytime sleepiness, unrefreshing naps, autonomic dysfunction, fatigue, and brain fog; nighttime signs and symptoms include long sleep, and sleep inertia. Symptom overlap between idiopathic hypersomnia and narcolepsy type 2 and the varied disease course of idiopathic hypersomnia present challenges in diagnosis. Furthermore, the diagnostic criteria for idiopathic hypersomnia are inadequate in their current form, and their use can lead to misdiagnosis and suboptimal treatment. The unclear pathophysiology of idiopathic hypersomnia and the absence of reliable biomarkers necessitate careful use of a variety of tests to make an accurate diagnosis. The Idiopathic Hypersomnia Severity Scale captures symptoms that distinguish idiopathic hypersomnia from narcolepsy, but this scale requires further evaluation in real-world populations and should be used with objective measures of sleep parameters and other validated instruments to accurately capture the full range of symptoms over a 24-hour period. This review describes a holistic view of the symptoms and impact of idiopathic hypersomnia, and frames diagnostic challenges and treatment considerations within the context of this view. Expert clinical opinion that aims to improve the diagnostic accuracy and treatment of idiopathic hypersomnia is provided.