Idiopathic hypersomnia (IH) is a rare neurological disorder. Treatment can help, but there’s no cure. You may snooze upwards of 9 hours a night without feeling refreshed. You may fight to wake up in the morning. Your sleepiness may persist or get worse, even when you take lengthy naps during the day.
If you live with IH, you’d probably like to know what’s causing your symptoms. Unfortunately, that’s not something experts have figured out yet.
“Literally, the name idiopathic hypersomnia means you’re sleepy and we don’t know why,” says Sabra Abbott, MD, assistant professor of neurology and sleep medicine at Northwestern University Feinberg School of Medicine in Chicago.
Lots of sleep specialists are trying to solve the IH puzzle, including Lynn Marie Trotti, MD, associate 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 Trotti says she and her colleagues still don’t know the main source of all this extra sleepiness.
“The big mystery really is what causes idiopathic hypersomnia,” Trotti says.
Theories Behind Idiopathic Hypersomnia
We don't yet know why people with IH are so sleepy, or why the disorder causes cognitive symptoms like brain fog, memory troubles, or poor attention. But thanks to ongoing research, Trotti and Abbott say there are some emerging clues, including:
Something triggers your GABA-A receptors. These are neurotransmitters that inhibit your central nervous system. Drugs like benzodiazepines can activate them. Doctors use these kinds of meds to treat anxiety and insomnia.
Trotti says people with IH sometimes have higher levels of natural benzodiazepines in their spinal fluid. “And the fact that there’s a difference suggests that (GABA-A receptors) might be related to the sleepiness in idiopathic hypersomnia,” she says.
There’s ongoing research into this theory. But Abbott says the idea is that something in your body acts like an all-day sleeping pill.
“That’s helpful for when you’re trying to go to sleep, but not when you’re trying to be awake during the day.”
Your circadian rhythm is out of sync. Everyone has a natural sleep-wake cycle. If you have IH, you might stay up late and have a lot of trouble waking up early. This “kind of suggests that there might at least be a component of a circadian timing issue,” Trotti says.
Abbott says she sees a lot of overlap between IH and something called delayed sleep-wake phase disorder. These are your natural night owls who fall asleep and get up later, she says. While the average circadian rhythm for most of us is just a little bit longer than 24 hours, she says this group operates differently.
“It’s sort of like they’re living a 25-hour day,” Abbott says. “Their sleep window is longer because their internal day is longer. They’re always playing catch-up.”
Chronic Fatigue vs. Idiopathic Hypersomnia
Since IH is a bit of a mystery, it can go undiagnosed for a long time. It can seem like other conditions. That might have something to do with how we think and talk about sleep. You might hear people use terms like "fatigue" and "sleepiness" interchangeably, but they aren’t the same thing.
Here’s how Trotti explains the difference: Hypersomnia means you either sleep too long or you fall asleep when you shouldn’t, such as taking naps during the day. Fatigue, on the other hand, is a weariness or lack of energy that doesn’t tend to raise your sleep time.
With that said, Trotti says about 20% of people with hypersomnia also have chronic fatigue syndrome. But a careful history of your symptoms can help your doctor figure out what’s going on.
They might ask:
- What do your night and day schedules look like?
- How much time do you spend asleep?
- How much time do you spend resting but awake?
- How much time do you spend trying to function while tired?
Sleep tests are also helpful. When it comes to hypersomnia, your doctor will see if:
- You fall asleep fast during a daytime nap
- You sleep more than 11 hours in a 24-hour period
Trotti says you wouldn’t expect the above symptoms if you have chronic fatigue syndrome without a hypersomnia disorder.
Where Is Research Headed?
Abbott says there’s a lot of interest in the GABA hypothesis. Most ongoing research is in that area because some anti-GABA drugs can reverse symptoms in some people with IH. In the future, there may be more drugs like this made specifically for IH.
“It’s a disorder we still don’t know a lot about and don’t have great treatments for,” Abbott says. “But as I tell my patients, there are people actively researching it. Hopefully, 5 or 10 years from now, we’re going to have better answers in terms of what causes it and what treats it.”
Lynn Marie Trotti, MD, associate professor, department of neurology, Emory University School of Medicine.
Sabra M. Abbott, MD, PhD, assistant professor of neurology, Center for Circadian and Sleep Medicine, Northwestern University Feinberg School of Medicine.
Sleep Medicine Clinics: “Idiopathic Hypersomnia.”
Genetic and Rare Diseases Information Center: “Idiopathic hypersomnia.”