Hypersomnia is a sleep disorder characterized by excessive daytime sleepiness despite having slept for an adequate or even prolonged amount of time at night. People with hypersomnia may sleep for 10 or more hours per night and still feel exhausted and unable to stay awake during the day. Unlike normal tiredness, the sleepiness associated with hypersomnia is persistent, difficult to manage, and significantly interferes with daily functioning. Hypersomnia can be primary or secondary. Primary hypersomnia is an intrinsic sleep disorder not caused by another condition; the most well-known form is idiopathic hypersomnia, a chronic condition with no identifiable cause. Secondary hypersomnia occurs as a result of another underlying condition, such as narcolepsy, sleep apnea, depression, hypothyroidism, neurological disorders, or the use of certain medications or substances. Common symptoms of hypersomnia include prolonged nighttime sleep, excessive and unrefreshing daytime sleepiness, difficulty waking up in the morning (sleep drunkenness), long and unrefreshing daytime naps, cognitive difficulties (often described as “brain fog”), memory impairment, and irritability. These symptoms can have a profound impact on work, social relationships, and quality of life. Diagnosis typically involves a clinical evaluation, sleep diary, and specialized tests such as polysomnography (an overnight sleep study) and the Multiple Sleep Latency Test (MSLT), which measures how quickly a person falls asleep in a quiet environment during the day. Treatment depends on the underlying cause and may include stimulant medications, lifestyle adjustments, and management of any contributing conditions. Consulting a sleep specialist is important for anyone experiencing persistent excessive daytime sleepiness.