Symptoms often develop slowly during adoescence or young adulthood. They include:

• Daytime naps that do not relieve drowsiness
• Difficulty waking from a long sleep -- may feel confused or disoriented
• Increased need for sleep during the day -- even while at work, or during a meal or conversation
• Increased sleep time -- up to 14 - 18 hours per day

Other symptoms may include anxiety, feeling irritated, low energy, restlessness, slow thinking or speech, loss of appetite, and memory difficulty.

Cataplexy -- suddenly falling asleep or losing muscle control -- which is part of narcolepsy, is NOT a symptom of idiopathic hypersomnia.

The health care provider will take a detailed sleep history. Tests may include:

• Multiple-sleep latency test
• Sleep study (polysomnography, done to identify other sleep disorders)

A psychiatric evaluation for atypical depression may also be done.