Abstract
Hypersomnolence is a clinically defined syndrome characterized by the association of prolonged nocturnal sleep, impaired arousal quality, and sleep inertia. Hypersomnolence is the major feature of central hypersomnias and is frequently reported in various mood disorders, such as major depressive disorder, bipolar disorder, or seasonal affective disorder. Assessment of hypersomnolence is challenging in depressed patients, with objective tests often in the normal range despite a high level of sleepiness complaint. On the other hand, many patients with central hypersomnias reported depressive symptoms. The self-assessment of mood symptoms in patients with central hypersomnias may overdiagnose depression with an overlap between both conditions.