Excessive daytime sleepiness is an essential feature of idiopathic hypersomnia, but other key symptoms and aspects of the medical history are crucial when evaluating patients who present with excessive daytime sleepiness. Patients with idiopathic hypersomnia commonly report the following symptoms in addition to excessive daytime sleepiness: severe and prolonged sleep inertia, long and unrefreshing naps, prolonged sleep time, and cognitive dysfunction.

Knowing the key symptoms and utilizing sleep testing can increase a healthcare professional’s confidence in his/her diagnosis of idiopathic hypersomnia.

The Idiopathic Hypersomnia Severity Scale is a 14-item questionnaire that is a clinical tool designed specifically to measure patients’ idiopathic hypersomnia symptoms and provide a touchpoint that might be useful for patient identification, follow-up visits, and idiopathic hypersomnia management.

This episode is produced by Sleep Review. It is episode 1 of a 5-part series sponsored by Jazz Pharmaceuticals. Visit Jazzpharma.com and SleepCountsHCP.com  for more information.

In episode 1, listen as Sleep Review’s Sree Roy and sleep specialist Logan Schneider, MD, discuss:

  • The symptom of idiopathic hypersomnia that people are most familiar with is excessive daytime sleepiness. Will you define and briefly explain this core symptom?
  • But excessive daytime sleepiness is not the only symptom typically reported by people with idiopathic hypersomnia. Prolonged sleep time is another common symptom. What can this mean over the course of a 24-hour day?
  • Sleep inertia, that feeling of difficulty waking up, can happen to all of us. How can sleep inertia differ in people with idiopathic hypersomnia versus in those without it?
  • Are naps generally restorative for people with idiopathic hypersomnia? Does length matter?
  • What ancillary cognitive symptoms are commonly reported with idiopathic hypersomnia?
  • In 2019, the Idiopathic Hypersomnia Severity Scale was developed to measure the severity, frequency, and functional impact of the key symptoms of excessive daytime sleepiness, prolonged nighttime sleep, and sleep inertia. What do you think is the clinical utility of this questionnaire?
Podcast Transcript

Sree Roy: 

Hello, and welcome. I’m Sree Roy with Sleep Review, and I’m thrilled to be here with sleep specialist Logan Schneider, MD, who is skilled in clinical research, medical education, epidemiology, sleep medicine, and neurology. He received postdoctoral training in sleep genetics and big data and has advised multiple startups in their sleep endeavors.  

This episode is sponsored by Jazz Pharmaceuticals.  

Today, we are chatting about the symptoms of idiopathic hypersomnia.  

The symptom of idiopathic hypersomnia that people are most familiar with is excessive daytime sleepiness. Will you define and briefly explain this core symptom? 

Dr. Logan Schneider: 

Sure, yeah. We all know sleepiness. We’ve all experienced it, obviously, particularly after a poor night’s sleep, but it becomes excessive when it’s to the point where you have difficulty staying awake and maintaining function, and it’s pervasive and happening on a chronic basis. Really, that’s how we define it from a clinically severe or clinically problematic standpoint, is not only are you excessively sleepy, like having had a bad night’s sleep, but even having had what we would all consider an adequate night’s sleep. You typically just cannot feel sufficiently awake, falling asleep at inappropriate times and in inappropriate settings. And so from that standpoint, the excessiveness of it is meaning that it encompasses much of your daytime waking function, and it’s impaired, you just can’t stay awake. 

And we typically define that clinically by the severity on various scales, like the Epworth Sleepiness Scale score, where we actually can determine how likely you are to doze off in various contexts, from relatively active contexts where you’re paying attention to somebody and having a conversation, to relatively sedentary and inactive contexts like watching a movie or sitting as a passenger in a car. And, the more likely you are to doze off in multiple different scenarios kinda gives us a gauge of how severely sleepy you are. And so that’s what excessive daytime sleepiness is. 

Sree Roy: 

But, excessive daytime sleepiness is not the only symptom typically reported by people with idiopathic hypersomnia. Prolonged sleep time is another common symptom. What can this mean over the course of a 24-hour day? 

Dr. Logan Schneider: 

Well, I think that’s the important thing to highlight, to determine when daytime sleepiness is excessive, and at that point becoming pathologic or reflective of an underlying disease, is the fact that everybody has sleepiness. And this is often why patients who ultimately end up with a diagnosis of idiopathic hypersomnia are often taking a long time to get to their diagnosis, is because most people don’t look at sleepiness as a clinical disorder.  

We’ve all experienced sleepiness, and so the solution is we’ll sleep more. The irony is that in patients with idiopathic hypersomnia, they actually come with a constellation of symptoms, one of which you just mentioned is often excessive amounts of sleep. And so they not only have excessive sleepiness, which is hypersomnolence, but they also have excessive need for sleep, which is how much they actually sleep on average or can sleep on average. 

And so, we can look at that in various contexts. One might be, if you’re clocking nine hours, that’s a lot, everyone would agree, but maybe that’s still insufficient for these folks. Some of these folks, if you ask them, not how much do you sleep because that’s often constrained by society and our social schedules. But if you ask them, “How much can you sleep?” they’re like, “Well, let me tell you…20 hours,” and that’s an inordinate amount of time for almost anybody to sleep, even after prolonged periods of chronic sleep restriction, which we all face on a daily basis. Sleeping in on days off, or holidays, or weekends, eventually we burn that out, and we get back to a stable amount of sleep. These folks never do.  

So they sleep, in prior criteria for diagnosing this order, we would have them more than 10 hours on average. These folks certainly do well in excess of that, both in their primary sleep period, which is usually at night, as well as through napping throughout the day can easily get up above 660 minutes, 11 hours or so in many cases. 

Some of those individuals who have idiopathic hypersomnia without long sleep time, are still sleeping quite a bit, typically, what we would consider adequate and possibly a bit more than the average person, even if still in the normal range, and despite that excessive amount of sleep, are still sleepy during the day. So that’s indicative of the fact that they’re sleeping more than you or I and still not functioning during the day, looking like you or I if we had chronic sleep restriction at five or six hours a night. 

So, in essence, it may be that their longer need is curtailed to what still looks long, and then they’re still sleepy during the day. And again, people reflect on that and say, “But you’re sleeping all the time. Why are you still sleepy?” And it’s like, that’s a disorder. 

Sree Roy: 

Sleep inertia, that feeling of difficulty waking up, can happen to all of us. How can sleep inertia differ in people with idiopathic hypersomnia versus in those without it? 

Dr. Logan Schneider: 

I think, again, this is the uniqueness of this disorder, and as you mentioned, we’ve all experienced sleep inertia or likely have experienced it at some point in our lifetime. And sometimes we even experience it as if we had idiopathic hypersomnia or one of these other hypersomnolence or hypersomnias, in the sense that you wake up and you don’t feel refreshed, and you’re kind of groggy, and it takes a while for thing the gears to get going. That’s kind of it, on certain circumstances. The best way to have experienced it is if you’ve ever had the unfortunate circumstance or if you wanted to test it out, wake up very shortly after having fallen asleep, within that maybe 30- to 60-minute time window where you’re in the deepest stages of sleep where normally you wouldn’t be able to wake up because you’re so soundly asleep, what we be able to typically call deep sleep. 

When you wake up from that stage of sleep, your brain is the most offline it can be. And you have this long period of coming to full alertness, because your brain has put such emphasis on trying to stay deeply asleep. And that phenomenon, is inertia. Just like inertia in the physical sense, it takes a long time for you to get out of that deep state of sleep state in your brain and actually come to a full level of alertness and cognitive functioning. And if you do it in the deepest stages of sleep early in your night, well then you’re most cognitively impaired, you’re most functionally impaired. Unfortunately, with folks with idiopathic hypersomnia, that’s their morning. 

They may have gone through an epic amount of sleep, 10 hours or so, and then they wake up and still have that, which is astounding. The average person, if we get the same amount of sleep as them, are not going to wake up like we just were woken up a couple of hours into sleep, but they do. And it typically lasts for quite some time, and they’ll even have it after periods of napping that are quite long during the day as well, where they should have burned off all of that sleep drive. 

So in essence, sleep inertia is really just the prolongation of that sleeping brain into the waking state, where you’re just not functioning well. You feel like people describe it sometimes as a sense of “brain fog,” which may be just sleep inertia pervading their entire day, or like they’re moving through molasses or something like that, where everything is just moving very slowly. And sometimes it can be so extreme, and occasional people have experienced this, where the sleep inertia is to the point where they actually don’t become fully conscious of their actions. Just like somebody who sleepwalks or is disturbed in the middle of their night of sleep and may have done something. Occasionally you’ve turned off your alarm and I don’t recall having turned off my alarm. That’s because of the amnesia associated with these deeper stages of sleep. 

Where these individuals with sleep inertia will be so impaired as to not remember what they’re doing or even do abnormal things, what we call automatic behaviors, where they might end up brushing their teeth with their hairbrush, or putting the wrong thing on their toothbrush to brush their teeth, or doing really odd behaviors that they just don’t even recall or just they look like somebody who’s not fully with it. So sometimes that that’s how severe the sleep inertia can be is it’s to the point of amnesia and automatic behaviors in their morning. 

So, there are varying degrees of this, and I’ve had that. In fact, I even woke up one night when I was in residency, medical residency training. I woke up the following morning after having been on a night of call, and the attending was asking about a note I had written, and I was like, “What are you talking about?” And he’s like, “Oh, this note, it’s hard to understand. It’s incoherent gibberish,” and I was like, “I didn’t write that note,” and he’s like, “You signed this note at 2:00 am,” and I said, “Oh.” I clearly woke up, answered a consult, wrote a note on the patient, signed it, and had gone back to sleep, all as an automatic behavior because I was so severely sleep-impaired throughout that period of my life that I actually never came to full consciousness and remembered that. And that’s an automatic behavior that many of us have had. A smaller proportion of people than have woken up groggy. 

So it just evidence is this is really an evidence of a severe sleep impairment, again, happening after often huge amounts of sleep on a chronic basis and on a given night, these people still wake up like that every day. 

Sree Roy: 

We’ll be right back with Dr. Schneider after the short break.  


This episode is sponsored by Jazz Pharmaceuticals. Jazz Pharmaceuticals is a global biopharmaceutical company with a focus in neuroscience and sleep medicine committed to improving the lives of patients and their families. Jazz is also the proud creator of SleepCountsHCP.com. The goal of SleepCountsHCP.com is to increase awareness of idiopathic hypersomnia and support symptom recognition, to help patients receive a quality diagnosis and appropriate disease management. SleepCountsHCP.com provides evidence-based educational materials and resources to improve communication between healthcare professionals and their patients. Visit Jazzpharma.com and SleepCountsHCP.com for more information. 


Sree Roy: 

Are naps generally restorative for people with idiopathic hypersomnia? Does length matter? 

Dr. Logan Schneider: 

So, similar to nighttime or typical sleep period sleep for folks with idiopathic hypersomnia, naps tend to  

not be very refreshing. And regardless of the duration of naps, but their naps tend to be quite long on  

the matter of hours. As they’re clocking well in excessive 11 hours in a given day, those naps are often making up for inadequacy of nocturnal sleep, or even if the nocturnal sleep or the primary sleep period is long, they’ll still take these long naps and wake up from them unrefreshed.  

And unrefreshed means, they’ll still have excessive daytime sleepiness afterward where they can fall asleep easily in various contexts, as well as typically waking up from those naps without that feeling of, “Oh, I just slept,” but again, having that sleep inertia on the other end, which I think is a characteristic of all sleep for these folks. They typically look at sleep with anxiety thinking, “Well, anytime I sleep, it’s just to wake up and fight the battle to be awake again after this anyhow.” So no aspect of refreshment is what they really are looking at when they lay their head down to get some rest. 

Sree Roy: 

What ancillary cognitive symptoms are commonly reported with idiopathic hypersomnia? 

Dr. Logan Schneider: 

Well, I think the most characteristic one is one I alluded to before, which is that sense of brain fog, where it seems like the brain is just not working. Some folks, each person really experiences this and describes it differently and has a different flavor of it, but brain fog I think is the most universally-recognized or reported one because I think it resonates with a lot of patients, where they’re just not seeming to operate on the same speed as everyone else’s brain. Kind of like moving at a slower pace, not connecting all of the dots, is kind of how it’s been described. And for some folks that can just be like they can just never get up to speed. For others, it actually can be this kind of a sense of fatigue, but a brain-based fatigue, a neurocognitive fatigue rather than a physical exertional fatigue. But when you’re exerting your brain thinking, at the same type of way that you would take a challenging test or test or run a marathon, a physical versus cognitive, these individuals can tire out much more readily. So the cognitive effort put into even mundane everyday tasks, it seems overwhelming and actually can burn them out much more quickly. 

So, those are the types of things is one, that they could just never get up to speed, but others that they may have the energy and endurance, but not the endurance, they may start off, but burn out more quickly or be run down more readily than you or I. 

Sree Roy: 

In 2019, the Idiopathic Hypersomnia Severity scale was developed to measure the severity, frequency, and functional impact of the key symptoms of excessive daytime sleepiness, prolonged nighttime sleep, and sleep inertia. What do you think is a clinical utility of this questionnaire? 

Dr. Logan Schneider: 

I think the questionnaire is quite good. Coincidentally, all of the publications on it, I happen to be tagged as a reviewer for. So, I’ve been able to do in-depth reading of it, and give feedback to the authors to, I believe, improve the value and applicability for individuals who use it. So I’ve been very fortunate to have been on that side of the understanding of how this has been developed.  

And I think it’s useful in the sense that heretofore, we have looked at idiopathic hypersomnia from the excessive daytime sleepiness or hypersomnolence lens, which again is hard. Many people just look at that and they say, “Why are you so sleepy? Just sleep it off,” and that’s what really the scale was trying to get at is looking at the characteristic of how we define these patients and their syndrome of symptoms, really a constellation of things that encompasses the nature and the variability of idiopathic hypersomnia. Recognizing not only that excessive sleepiness, the hypersomnolence, which is the Epworth Sleepiness Scale score and how we often identify these folks, but also that excessive need for sleep, and how that has impact on daytime function. 

So it’s really talking about that long sleep time, sleep inertia component. It’s talking about that napping component. It’s talking about that function, cognitive function, physical function during the day. Those major three dimensions is how they’ve encapsulated it, and they’ve taken a look specifically at that type of sleepiness in idiopathic hypersomnia, compared to sleepiness from other causes. So it’s really a useful tool for not only encapsulating all of those different characteristics that feed into this condition and differentiate it from just being sleepy, particularly being sleepy for other reasons, like inadequate sleep or sleep disorders, but also does a good job of giving you some degree of severity and a way to quantify how bad these individuals are suffering or how badly they’re suffering, so that the higher the score, you have an idea, “Oh man, this person is much more functionally impaired over their 24 hours.” And then, it gives you also a great way of tracking these things over time to say, “Oh, and we’ve made improvements. The score has gone down and gotten you closer to looking like a more normal individual from a sleep standpoint.” 

So, for many reasons, having an instrument like that is great because it really is tied to this disorder and differentiates it from other reasons of sleepiness, and then also gives you an idea of how severe it is. 

Sree Roy: 

Thanks so much for chatting with us about the symptoms of idiopathic hypersomnia. You can find Sleep Review at sleepreviewmag.com. Thank you so much for tuning in to this episode. 


To dive even deeper:


Trotti LM. Idiopathic hypersomniaSleep Med Clin. 2017;12(3):331-44.

Dauvilliers Y. Idiopathic hypersomnia severity scale. 2018.

Arnulf I, Leu-Semenescu S, Dodet P. Precision medicine for idiopathic hypersomniaSleep Med Clin. 2019;14(3):333-50.

Vernet C, Leu-Semenescu S, Buzare MA, Arnulf I. Subjective symptoms in idiopathic hypersomnia: beyond excessive sleepinessJ Sleep Res. 2010;19(4):525-34.

Dauvilliers Y, Evangelista E, Barateau L, et al. Measurement of symptoms in idiopathic hypersomnia: The Idiopathic Hypersomnia Severity ScaleNeurology. 2019;92(15):e1754-62.

Rassu AL, Evangelista E, Barateau L, et al. Idiopathic Hypersomnia Severity Scale to better quantify symptoms severity and their consequences in idiopathic hypersomniaJ Clin Sleep Med. 2022;18(2):617-29.

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