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Hypersomnia refers to the condition of sleeping excessive amounts. However, in current medical terminology, both “hypersomnia” and the related word “hypersomnolence” are used more broadly to indicate long sleep durations, excessive daytime sleepiness, or both. In some classification systems (such as the ICSD-3, which the HF follows), “hypersomnia” is reserved to refer to specific disease entities, such as idiopathic hypersomnia and the related sleep disorders, while “hypersomnolence” refers to the symptoms of long sleep and/or excessive daytime sleepiness regardless of cause. For more details, see Classification of Hypersomnias.

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