Unexplained hypersomnia (excessive daytime sleepiness)


Unexplained hypersomnia (excessive daytime sleepiness)


The word 'hypersomnia' means excessive sleep or sleepiness that interferes with everyday life.

There are many possible causes, including medical conditions such assleep apnoea or restless legs syndrome that interfere with night-time sleep, severe sleep deprivation, depression, certain medications (such as tranquillisers), drug and alcohol misuse, or a previous head injury. 

However, some people with hypersomnia will not have an underlying medical condition and there will be no obvious explanation for it – they have it despite normal quantity and quality of sleep. These mystery rare cases are known as 'idiopathic' or primary hypersomnia.

The rest of this page focuses on idiopathic hypersomnia. 

What are the symptoms of idiopathic hypersomnia?

People with idiopathic hypersomnia struggle so much to stay awake during the day, they are compelled to take frequent long naps. These may be at inappropriate times, such as during a conversation or meal, or while driving.

Naps tend not to provide any relief from the sleepiness – someone with idiopathic hypersomnia rarely feels refreshed.

As well as sleeping throughout the day, most people with the disorder usually sleep for more than 10 hours a night and struggle to wake in the morning because they feel very drowsy and confused upon waking ('sleep drunkenness'). The quality of sleep in idiopathic hypersomnia is generally very good.

Someone with idiopathic hypersomnia may also:

have mental health problems such as anxiety or depression

lose their appetite

have low energy

be restless or agitated

think or speak slowly

have trouble remembering

These symptoms often develop during adolescence or in the early twenties, although they can occur later in life. It's unusual for the condition to spontaneously improve.

A rarer form of the disease means you'll have the same daytime sleepiness but will sleep for a normal amount of time at night (about eight hours) and be able to wake normally.

Idiopathic hypersomnia is similar to narcolepsy in that both can cause you to fall asleep at any time, but there are distinct differences (see box, left).

What should I do?

If you're constantly drowsy during the day and are concerned because it's affecting your everyday life, see your GP. They'll want to know about your sleeping habits, how much sleep you get at night, if you wake during the night and whether you fall asleep during the day.

Your doctor will also want to know if you have any emotional problems such as depression or take any drugs that may be interfering with your sleep, which could explain your hypersomnia. 

They may order tests to see if your sleepiness could be caused a sleep disorder or whether there are other factors that could lead to hypersomnia.

Depending on your symptoms, you may be asked to have a couple of sleep assessments:

Polysomography (a night-time sleep test), which will help rule out possible sleep disorders such as narcolepsy or obstructive sleep apnoea. You stay in a special bedroom and are observed from another room through the night. Electrodes are attached to your face, head and body to record brainwaves, muscle activity and eye movement. Your breathing and snoring are also monitored. 

Multiple sleep latency test – this test usually follows the next day. You're asked to sleep on four or five occasions at 2-hour intervals throughout the day, so doctors can see how long it takes you to fall asleep (it shouldn't take longer than eight minutes for someone with hypersomnia).

Making a diagnosis

Doctors will diagnose idiopathic hypersomnia if you have excessive daytime sleepiness for at least one month and need almost daily daytime sleeps, and no other causes have been found.

Idiopathic hypersomnia is usually only diagnosed if you fall asleep in less than eight minutes in all the nap opportunities without experiencing 'dream sleep' (rapid eye movement sleep, or REM sleep). Entering dream sleep in daytime naps is more characteristic of narcolepsy.

What causes idiopathic hypersomnia?

There is no underlying medical problem or obvious cause for idiopathic hypersomnia. The daytime sleepiness happens despite normal quality and quantity of sleep.

It is thought this is caused by a problem with the brain systems that regulate when we sleep and wake.

Researchers believe that someone with idiopathic hypersomnia will produce too much of a molecule called GABA, which is involved in sedation. The effect is like being permanently medicated with sleeping pills or alcohol.

How is idiopathic hypersomnia treated?


There are no licensed medicines to treat idiopathic hypersomnia.

Medications licensed for use in narcolepsy are usually prescribed, but may not work as well for idiopathic hypersomnia as they do for narcolepsy. They include the stimulant medicines amphetamine, methylphenidate and modafinil.

Very recently, a medicine called flumazenil has been shown to help some patients with idiopathic hypersomnia, although more research is needed to be sure of its effectiveness. Flumazenil is normally used to stop the effects of benzodiazepines, a type of medicine used to treat sleeping problems or anxiety. It's used to stop the effects of taking too much of these types of medicines or to wake people up after they have had benzodiazepines for sedation during minor surgery or other procedures.

Antidepressants may be prescribed if emotional problems are interfering with your sleep.

Lifestyle changes

It should help to avoid alcohol, caffeine and medications that make the condition worse, and to avoid working at night or engaging in social activities that delay bedtime.

Related information 

Read about the:

treatment of narcolepsy

treatment of sleep apnoea

treatment of depression






Idiopathic hypersomnia vs narcolepsy


The sleep disorder narcolepsy can also cause excessive daytime sleepiness and falling asleep at virtually any time, but it is not the same as idiopathic hypersomnia:

In narcolepsy, you may lose muscle control when experiencing strong emotions (cataplexy) – this does not happen in idiopathic hypersomnia.

People with narcolepsy often have very vivid dreams and even hallucinations when they are drowsy, which are generally not seen in idiopathic hypersomnia.

The overnight sleep in narcolepsy is usually very fragmented and or poor quality, unlike typical cases of idiopathic hypersomnia.

Short daytime naps in narcolepsy tend to be refreshing – naps in idiopathic hypersomnia are more like long sleeps and are not refreshing.

In idiopathic hypersomnia, you do not go quickly into rapid eye movement (REM) or dream sleep, which you do with narcolepsy.