• Overwhelming need for excessive sleep. Despite adequate and often extraordinary amounts of good quality sleep (e.g., 10–11 hours or more per night), people with IH still feel excessively sleepy during the day.
   

• Chronic excessive daytime sleepiness, often resulting in long daytime naps.
   

• Long and unrefreshing naps. Naps are usually more than one hour long and are typically not refreshing.
   

• Extreme and prolonged difficulty waking up with an uncontrollable desire to go back to sleep. It is accompanied by confusion, irritability, and poor coordination, e.g., dropping things, walking into doorways. Speech may also be slow or slurred. It can also include automatic behaviour, i.e., performing tasks without consciously knowing it and not remembering you have done them, e.g., turning off alarm clocks or answering your phone.
   

• Cognitive dysfunction (commonly referred to as ‘brain fog’): problems with memory, concentration and attention, and automatic behaviour.
   

In an attempt to combat the overwhelming sleep pressure, people with IH may develop ADHD-like symptoms such as fidgeting and talking a lot.

Additionally, autonomic dysfunction, a condition affecting the nervous systems control of automatic functions, is common in IH. This can manifest as headaches, dizziness upon standing, and trouble regulating body temperature.
 

Many people with IH regularly sleep more than 10–11 hours out of every 24. Despite good-quality sleep, it is not refreshing. Sleep is generally deep, and waking up can be extremely difficult. Sleep inertia, which is extreme difficulty awakening from sleep, can be so severe in people with IH that they sleep through multiple loud alarms and may even fall back to sleep several times. They often require humans to wake them and make sure they stay awake.

Sleep drunkenness is typically experienced with sleep inertia. Sleep drunkenness consists of confusion, disorientation, poor motor coordination, and slowness. People with sleep drunkenness may say irrational or unintentional things. Their speech may be slow or slurred. They may be clumsy, e.g., drop things, walk into doorways, or bounce off walls. Some people report sleep drunkenness lasting as much as 4 hours or more and that it can sometimes be more problematic than the chronic daytime sleepiness in IH. Those that experience sleep inertia or sleep drunkenness usually experience it every time they wake up, i.e., in the morning and when waking up from naps. People with IH commonly say that they never feel fully awake and that they struggle with a constant mental fogginess that can make carrying out even basic tasks difficult. Learn more about sleep drunkenness and sleep inertia here

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Symptoms frequently appear in the mid-to-late teens or early twenties. IH is a chronic disorder with limited treatment options. Medications do not treat the cause, are often not very effective, and can cause intolerable side effects. Even with medication, people with IH may struggle with ordinary day-to-day activities. Learn more about managing IH here.