Idiopathic Hypersomnia causes more than just sleepiness
- Feb 5
- 4 min read
Articled update: May 2026 - new research added
The main symptom of Idiopathic Hypersomnia (IH) is an 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 are in an almost constant state of sleepiness. But IH is much more than that.
New research continues to reinforce what people living with IH have been trying to explain for years:
Idiopathic Hypersomnia is a 24-hour disorder.
IH affects people across the entire day and night.
Brain fog & cognitive dysfunction
IH affects cognitive function, including problems with memory, concentration, attention, processing speed and mental clarity. Many people describe this as “brain fog”.
This cognitive dysfunction can affect:
Work and study
Daily functioning
Driving
Social interaction
Emotional wellbeing
Importantly, these difficulties often persist even when people are being treated with medication.
Sleep drunkenness / severe sleep inertia
People with IH can experience extreme and prolonged difficulty waking up, accompanied by confusion, irritability, poor coordination, and an uncontrollable desire to go back to sleep.
Speech may be slow or slurred. Some people sleep through multiple alarms, unknowingly turn alarms off, answer phone calls, or have conversations they later have no memory of.
Because of the severity of sleep inertia (sometimes referred to as sleep drunkenness), many people with IH need assistance waking up and remaining awake long enough to take medication.
Long sleep time & unrefreshing sleep
One of the most misunderstood aspects of IH is that people can sleep for extraordinarily long periods of time and still wake feeling unrefreshed.
Unlike in people without IH, people with IH typically do not wake up feeling refreshed, regardless of how long they sleep.
The recent review paper Idiopathic hypersomnia is a 24-hour disorder highlights that IH affects the entire 24-hour sleep–wake cycle and reinforces that symptoms extend far beyond excessive daytime sleepiness alone.
The paper also highlights variability within IH itself, including evidence that IH with long sleep time may be associated with:
worse fatigue,
longer and more frequent unrefreshing naps,
and greater autonomic dysfunction such as dizziness, temperature dysregulation, digestive issues, allergies and headaches.
Fatigue & autonomic dysfunction
People with IH may also experience:
Headaches
Dizziness on standing
Problems with temperature regulation
Digestive issues
Fatigue and physical heaviness
Autonomic dysfunction
These symptoms have been reported across multiple studies and patient registries and further reinforce that IH is not simply “being sleepy.”
Hyperactivity & compensatory behaviours
Some people with IH develop ADHD-like behaviours such as fidgeting, constant movement or excessive talking in an attempt to fight the immense sleep pressure associated with the disorder.
This can sometimes lead to misunderstanding or misinterpretation of symptoms.
IH impacts every aspect of life
The effects of IH extend far beyond sleep itself.
Research continues to show significant impairment across multiple quality-of-life domains, including:
Physical functioning
Emotional wellbeing
Social functioning
Cognitive ability
Work productivity
Relationships
Daily activities
The ARISE study highlighted the substantial burden IH places on people’s lives, despite most participants already being treated with medications. Researchers concluded that currently available treatments are often insufficient to adequately manage symptoms for many people living with IH.
As researchers from the recent 24-hour disorder review explain:
“Awareness of this around-the-clock disorder may help improve diagnostic accuracy, inform appropriate treatment choices, and provide a better understanding of the effects of treatment on symptom management.”
The authors also emphasised an important point:
“No single test captures the full impact of IH.”
Assessment and treatment therefore need to consider the entire 24-hour picture - not just excessive daytime sleepiness in isolation.
References:
Foldvary-Schaefer N, Maski K, Schneider LD, et al. Beyond daytime sleepiness in idiopathic hypersomnia. Sleep and Vigilance. 2025. https://link.springer.com/article/10.1007/s44470-025-00007-1
Schneider LD, Stevens J, Husain AM, et al. Symptom severity and treatment satisfaction in patients with idiopathic hypersomnia: the real world idiopathic hypersomnia outcomes study (ARISE). Nat Sci Sleep. 2023;15:89–101. doi:10.2147/NSS.S386021 Trotti LM, Ong JC, Plante DT, Friederich murray C, King R, Bliwise DL. Disease symptomatology and response to treatment in people with idiopathic hypersomnia: initial data from the Hypersomnia Foundation registry. Sleep Med. 2020;75:343–349. doi:10.1016/j.sleep.2020.08.034
Nevsimalova S, Susta M, Prihodova I, Maurovich Horvat E, Milata M, Sonka K. Idiopathic hypersomnia: a homogeneous or heterogeneous disease? Sleep Med. 2021;80:86–91. doi:10.1016/j.sleep.2021.01.031 Ozaki A, Inoue Y, Nakajima T, et al. Health-related quality of life among drug-naive patients with narcolepsy with cataplexy, narcolepsy without cataplexy, and idiopathic hypersomnia without long sleep time. J Clin Sleep Med. 2008;4(6):572–578. doi:10.5664/jcsm.27352
Vernet C, Leu-Semenescu S, Buzare MA, Arnulf I. Subjective symptoms in idiopathic hypersomnia: beyond excessive sleepiness. J Sleep Res. 2010;19(4):525–534. doi:10.1111/j.1365-2869.2010.00824.x Vignatelli L, D’Alessandro R, Mosconi P, et al. Health-related quality of life in Italian patients with narcolepsy: the SF-36 health survey. Sleep Med. 2004;5(5):467–475. doi:10.1016/j.sleep.2004.04.003
Dauvilliers Y, Paquereau J, Bastuji H, Drouot X, Weil JS, Viot-Blanc V. Psychological health in central hypersomnias: the French Harmony study. J Neurol Neurosurg Psychiatry. 2009;80(6):636–641. doi:10.1136/jnnp.2008.161588
Bušková J, Novák T, Miletínová E, et al. Self-reported symptoms and objective measures in idiopathic hypersomnia and hypersomnia associated with psychiatric disorders: a prospective cross-sectional study. J Clin Sleep Med. 2022;18(3):713–720. doi:10.5664/jcsm.9702
