Which disorder is associated with excessive sleepiness even after getting sufficient sleep?

Hypersomnolence Disorder is characterized by excessive sleepiness that persists despite obtaining an adequate amount of sleep. Individuals with this disorder may experience prolonged nighttime sleep or excessive daytime sleepiness, leading to difficulties in functioning during the day. This condition is distinct from other sleep disorders that may involve difficulties with initiating or maintaining sleep or disrupted sleep patterns. Instead, those with Hypersomnolence Disorder often report that they sleep well through the night yet continue to feel unrefreshed and excessively sleepy during waking hours.

In contrast, Insomnia Disorder involves difficulty falling asleep or staying asleep, resulting in insufficient sleep and daytime impairment. Obstructive Sleep Apnea Hypopnea is marked by repeated interruptions in breathing during sleep, leading to fragmented sleep and subsequent daytime sleepiness, but the key factor is the disordered nature of the sleep rather than the amount. Circadian Rhythm Sleep-Wake Disorders pertain to misalignments between an individual's internal sleep-wake cycle and the external environment, often leading to challenges in maintaining sleep at desired times rather than excessive sleepiness during the day after sufficient sleep. Thus, the defining feature of Hypersomnolence Disorder is the excessive sleepiness experienced despite adequate sleep duration.