Idiopathic hypersomnia

Idiopathic hypersomnia (IH) is a long-lasting (chronic) sleep disorder of the brain (neurologic disorder). Idiopathic means doctors don’t know what causes it. 


  • Affects the brain’s ability to control sleep and wakefulness
  • Causes excessive daytime sleepiness (EDS) — a strong daytime sleepiness or need to sleep during the day, even with enough sleep the night before  

People who have IH may spend most of their day either sleeping or thinking about, craving, or even fighting the urge to sleep, which can severely impact their quality of life.

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What are the symptoms of IH?

The main symptom of IH is EDS that lasts for at least 3 months. Sleep patterns may also change. People who have IH may often need 1 or more long naps (of 1 hour or more) a day, and their sleep is often unrefreshing. They may also need to sleep several hours more than the average person. 

Common symptoms include:

  • EDS — Excessive daytime sleepiness
  • Needed naps — 
    • Usually long (more than 1 hour)
    • Usually unrefreshing (non-restorative) and may make people feel even worse
    • May be hard or impossible to avoid
  • Brain fog — Feeling mentally sluggish or fuzzy, confused, forgetful, or unable to focus
  • Long sleep — Needing at least 11 hours of sleep per 24-hour period (including naps) or more than 9 hours at night (or whenever you sleep the longest)
  • Severe sleep inertia (or sleep drunkenness) —
    • Difficult to wake — may need multiple loud alarms or to have a supporter help with waking
    • Struggling to wake up fully, often with an overwhelming desire to go back to sleep
    • Feeling disoriented, confused, or irritable
    • Having poor coordination
    • Doing tasks without realizing it 
    • May last for a few hours after waking up
  • Unrefreshing sleep (or non-restorative sleep) — Waking up feeling like you haven’t slept
  • Sleep attacks — Episodes when you fall asleep in places or at times you don’t want to
  • Fatigue
    • A lack of physical or mental energy
    • Feeling tired or exhausted

You don’t need to have all of these symptoms to be diagnosed with IH, but you’ll have at least some of them. 

At what age do IH symptoms usually start?

Symptoms most often start in a person’s mid-to-late teens or early twenties. However, they can start at any age. They may start suddenly or develop over time. 

Symptoms may:

  • Happen every day, or a few days a week
  • Get worse or better over hours, weeks, months, or years

If you have IH, you may have times when you can function (do daily activities such as work or school) well or well enough, and other times when you don’t function well at all. Even if you function well at times, your symptoms should be taken seriously.

How do IH symptoms compare to narcolepsy types 1 and 2 symptoms?

Visit our web page: “Compare symptoms of idiopathic hypersomnia and narcolepsy types 1 and 2.”

How common is IH?

It’s hard to know how many people have IH. Some researchers have estimated 1 in every 50,000 people have IH. Other researchers have estimated 1 in every 3,000 people have IH.

Can IH go away on its own?

A few studies of people with IH have reported that the likelihood of IH going away on its own (the remission rate) is 10% to 33% (1 to 3 in every 10 people). However, because the cause of IH isn’t known and diagnosis can be unclear, some or all people whose IH went away might just have been initially misdiagnosed with IH. They may have actually had other conditions that were causing their excessive daytime sleepiness.

What’s it like to have IH?

Having IH can greatly affect daily life:

  • Waking up is usually very hard, especially for people who have IH with long sleep. They often need multiple alarms and morning rituals to wake up for school or work.
  • The amount and timing of needed sleep can limit daily activities.
  • IH can cause problems with thinking, working, and socializing. People with IH may have trouble doing their jobs, staying in school, having romantic relationships, and fully engaging with their friends and loved ones. 

These effects are especially true for people who aren’t taking medicines that work well. But even with medicines, people who have IH may struggle with these activities.

Stories from people living with IH

Two members of our community have made videos to explain what it’s like to have IH. While almost everyone with IH has EDS and brain fog, not everyone has the other symptoms, and they can affect each person differently.

Meghan has IH with long sleep time. For Meghan, the hardest thing is waking up every day.

Michelle has IH without long sleep time overlapping with narcolepsy type 2. For Michelle, the hardest thing is struggling with severe brain fog during the day.

Meghan has IH with long sleep time. For Meghan, the hardest thing is waking up every day.

2020 October – Meghan Mallare – “Sleeping My Life Away” – Video courtesy of Meghan Mallare

Michelle has IH without long sleep time overlapping with narcolepsy type 2. For Michelle, the hardest thing is struggling with severe brain fog during the day.

2020 October – Michelle Emrich, MD – “A Doctor’s Once Agile Brain Broken by IH” – Video courtesy of Michelle Emrich

Find more personal journey stories on our web page “What’s it like to live with a hypersomnia?

Find quotes about living with IH on our web page “Educating others about your sleep disorder.”

How will doctors know if I have IH?

Doctors will usually:

  1. Ask about your symptoms and medical history, sometimes using questionnaires
  2. Confirm from your history that you’ve had daily EDS for at least 3 months
  3. Do a complete physical exam and medical tests, including sleep studies, to make sure your EDS isn’t caused by something else

Common causes of EDS other than IH include: 

Testing for hypersomnia sleep disorders almost always includes a 2-part sleep study:

  1. An overnight sleep study measures several features of sleep and helps rule out other sleep problems such as sleep apnea. 
  2. A daytime nap study called a Multiple Sleep Latency Test (MSLT) measures how long it takes you to fall asleep during 4 or 5 nap opportunities (chances to nap). The MSLT also shows if you have REM sleep within 15 minutes of falling asleep during a nap. Doctors will usually diagnose you with IH if:
    • You fall asleep in 8 minutes or less (on average across all nap opportunities), and 
    • You have no more than 1 episode of REM sleep within 15 minutes of falling asleep (including your overnight sleep study)

If your 2-part sleep study doesn’t show IH, doctors can still diagnose you with IH if you average 11 hours or more sleep per day. To test this, you’ll usually wear an actigraph and keep a sleep diary for at least 7 days. 

You may need to prepare during the weeks leading up to your sleep studies, and your doctor may recommend that you change or stop taking specific medicines. Ask for time off from school or work if your symptoms are likely to keep you from being able to function well while you prepare. This may happen if you need to: 

  • Get much more sleep than you usually do
  • Change from a shift work schedule to a normal schedule
  • Stop medicines that are helping your symptoms
    • You may need to slowly taper off some medicines, such as antidepressants, and it may take longer for you to stop them before your sleep study and then get back up to a dose that works well for you after your sleep study

To learn more, visit our web pages: 

When should my doctor repeat my sleep studies?

  • Only repeat sleep studies if absolutely necessary — for example, if your symptoms have changed a lot and your doctor thinks your diagnosis has also changed.
  • If your insurer asks for repeat sleep studies, ask your doctor if the test is needed (“medically indicated”). Your doctor can also recommend different testing, which may include actigraphy and a more detailed sleep diary.

What can help my symptoms?

Visit our web pages:


Read or print out our summary of IH: Idiopathic Hypersomnia Characteristics and Diagnostic Criteria (PDF). You may want to share this summary with your doctors or others.

For more information, visit our web page for doctors: “Diagnosis, classification, symptoms, and causes of hypersomnias.”

Published Mar. 18, 2020 |
Revised Jan. 30, 2024
Complete update Jan. 19, 2024 |
Approved by our medical advisory board