This excessive sleepiness is accompanied by at least one of the following symptoms:
- Recurrent naps during the day, in excess of what would be expected for the child's normal developmental level
- A main sleep episode that is experienced as nonrestorative (not refreshing) despite lasting for an extended period
- Sleep inertia, impaired alertness, or difficulty being fully awake after abruptly awakening
Sleep inertia, sometimes called sleep drunkenness, is not required for a diagnosis of hypersomnolence, but is relatively specific to the disorder. Sleep inertia is characterized by disorientation or impaired alertness during the sleep-wake transition. During this time, which may last several minutes to several hours, the individual appears awake but exhibits impaired motor dexterity, memory deficits, inappropriate behavior, or disorientation.
Occasional sleep difficulties are fairly common in children and adolescents. Therefore, hypersomnolence disorder is diagnosed only when the sleep difficulty occurs at least three times per week for a period of three months or longer. Hypersomnolence disorder is diagnosed only if the individual is significantly distressed or impaired by the hypersomnolence or accompanying symptoms.