Symptoms

Idiopathic hypersomnia (IH) is a neurological sleep disorder characterized primarily by excessive daytime sleepiness and difficulty waking up, even after a full night of sleep. The symptoms typically develop slowly and can significantly impair daily functioning. Key symptoms include:

• Excessive daytime sleepiness: A persistent and overwhelming need to sleep during the day, often making it difficult to stay awake and alert even after adequate nighttime sleep.

• Long sleep duration: Sleeping more than 11 hours in a 24-hour period, sometimes up to 14-18 hours, without feeling refreshed upon waking.

• Difficulty waking up (sleep inertia or “sleep drunkenness”): People with IH often struggle to fully wake up and may feel groggy, confused, disoriented, or slow in thinking and movement after sleep or naps. They may require multiple loud alarms or assistance to wake up.

• Unrefreshing naps: Naps usually last longer than an hour but do not alleviate sleepiness or restore alertness.

• Cognitive impairment: Problems with memory, attention, brain fog, slow thinking or speech, and difficulty with coordination are common.

• Automatic behaviors: Some individuals may perform activities automatically (e.g., driving without awareness, writing or speaking without recollection) during episodes of extreme sleepiness.

• Additional symptoms: Anxiety or irritability after waking, headaches, dizziness or lightheadedness when standing up, temperature regulation issues (feeling too hot or cold), and occasionally sleep paralysis or hallucinations around sleep transitions.

• Rare sudden sleep episodes: Unlike narcolepsy, sudden sleep attacks are uncommon but can occur in some cases.