Idiopathic hypersomnia (IH) is a rare neurological disorder. Treatment can help, but there is no cure. You can snooze for more than 9 hours a night without feeling refreshed. You may struggle to get up in the morning. Your drowsiness may persist or get worse, even when you take long daytime naps.
If you live with IH, you will likely want to know the cause of your symptoms. Unfortunately, that’s not something experts have discovered yet.
“The name idiopathic hypersomnia literally means you’re sleepy and we don’t know the cause,” says Sabra Abbott, MD, assistant professor of neurology and sleep medicine at Northwestern University School of Medicine in Chicago.
Lots of sleep professionals are trying to solve the IH puzzle, including Lynn Marie Trotti, MD, assistant professor of neurology at Emory University School of Medicine in Atlanta. Sleep disorders tend to run in families, so your genes likely have something to do with it. But Trouti says she and her colleagues still don’t know the main source of all that extra sleepiness.
“The big mystery is what causes idiopathic hypersomnia,” Trotti says.
Theories behind idiopathic hypersomnia
We don’t yet know why people with IH feel so sleepy, or why the disorder causes cognitive symptoms like brain fog, memory problems, or poor attention. But thanks to ongoing research, Trouti and Abbott say there are some clues emerging, including:
Something is firing your GABA-A receptors. These are neurotransmitters that suppress the central nervous system. Medicines such as benzodiazepines can activate them. Doctors use these types of medications to treat anxiety and insomnia.
Trouti says that people with IH sometimes have higher levels of natural benzodiazepines in their spinal fluid. “The fact that there is a difference suggests that[GABA-A receptors]may be associated with sleepiness in idiopathic hypersomnia,” she says.
There is ongoing research into this theory. But Abbott says the idea is that something in your body acts like a sleeping pill all day long.
“This is useful when you are trying to sleep, but not when you are trying to be awake during the day.”
Your circadian rhythm is out of sync. Everyone has a normal sleep-wake cycle. If you have IH, you may stay up late and have a lot of trouble getting up early. “This kind of signal suggests that there may be at least one component of the diurnal timing problem,” Trotti says.
Abbott says she sees a lot of overlap between IH and something called delayed sleep-wake phase disorder. These are normal night owls that sleep and wake up later, she says. While the average circadian rhythm for most of us is a little longer than 24 hours, she says this group works differently.
“It’s like they live 25 hours a day,” Abbott says. “Their sleeping window is longer because their indoor day is longer. They are always playing catch-up.”
Chronic fatigue vs. idiopathic hypersomnia
Because IH is somewhat of a mystery, it may remain undiagnosed for a long time. It can look like other terms. It may have something to do with how we think and talk about sleep. You may hear people use terms like “fatigue” and “drowsiness” interchangeably, but they are not the same thing.
Here’s how Trouti explains the difference: Hypersomnia means that you either sleep too long or sleep when you shouldn’t, like taking naps during the day. On the other hand, fatigue is fatigue or a lack of energy that does not increase your sleep time.
However, Trouti says about 20% of hypersomnias also have chronic fatigue syndrome. But a careful history of your symptoms can help your doctor know what’s going on.
They may ask:
- What do the day and night schedules look like?
- How much time do you spend sleeping?
- How much time do you spend resting but are awake?
- How much time do you spend trying to work when you are tired?
Sleep tests are also helpful. When it comes to hypersomnia, your doctor will see if it:
- Fall asleep quickly during a daytime nap
- You sleep more than 11 hours in a 24 hour period
Trouti says you wouldn’t expect the above symptoms if you had chronic fatigue syndrome without hypersomnia.
Where is the search headed?
Abbott says there is a lot of interest in the GABA hypothesis. Most of the ongoing research is in this area because some anti-GABA medications can reverse symptoms in some people with IH. In the future, there may be more similar medications designed specifically for IH.
“It’s a disorder that we still don’t know much about and we don’t have good treatments for,” Abbott says. “But as I tell my patients, there are people who are actively looking for it. Hopefully, 5 or 10 years from now, we will have better answers in terms of what causes it and what treats it.”