Ask the Doctor: IH, CFS and Fibromyalgia – How Do They Differ?

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Lynn Marie Trotti, MD, MSc, of Emory University, and the Chair of our MAB

What’s the difference between chronic fatigue syndrome (CFS) and idiopathic hypersomnia (IH)? How do they differ from fibromyalgia? And how many people with IH also have CFS or fibromyalgia? A medical expert explains! We are very pleased to have Lynn Marie Trotti, MD, MSc, of Emory University, and the Chair of our Medical Advisory Board, answer these questions.

QUESTION: What’s the difference between chronic fatigue syndrome (CFS) and idiopathic hypersomnia (IH)? Is it just sleep attacks? Or is it part of the differential diagnosis? What about fibromyalgia? How does the medical community differentiate between these 3 diseases? How many patients with IH ALSO have fibromyalgia or CFS?

ANSWER: Idiopathic hypersomnia is defined by its pathologic degree of sleepiness, which implies too much or inappropriate sleep, either because of long sleep times at night or unavoidable sleep during the day.1 Chronic fatigue is defined by its pathologic degree of fatigue, which implies exhaustion or weariness but without long sleep bouts or irresistible daytime sleep. It can be difficult to distinguish between sleepiness and fatigue, especially because words like “tired” can indicate either condition, and so IH and CFS are part of each other’s differential diagnosis. However, careful discussion of symptoms and several types of sleep testing can help with this discussion.

Symptoms that are common in idiopathic hypersomnia, in addition to sleepiness, include difficulty waking up (called sleep inertia or sleep drunkenness), long sleep times at night, and long naps that don’t improve symptoms.1 These symptoms are not classic symptoms of chronic fatigue. In contrast, a common symptom in chronic fatigue syndrome is post-exertional worsening of fatigue, meaning that exertion such as a work-out makes the fatigue much worse;2 people with IH typically do not notice drastic worsening of sleepiness in response to this type of exertion. Some symptoms, such as a feeling of “brain fog” and lightheadedness with standing, are common in both IH and chronic fatigue, and don’t help doctors make this distinction.

Diagnosis of IH also requires sleep testing. This can include any of three tests: a multiple sleep latency test, a 24-hour sleep study, or actigraphy (a medical-grade FitBit-like device). At least one of these three tests usually is abnormal in people with IH. These tests have not been studied as extensively in people with chronic fatigue, as none of these tests are used for chronic fatigue diagnosis.

Making matters more complicated, people with idiopathic hypersomnia, narcolepsy, and other disorders of excessive daytime sleepiness commonly experience fatigue in addition to sleepiness. Approximately 20% of people with these sleep disorders will also meet diagnostic criteria for CFS.3 This might be because they have two disorders, e.g., both IH and chronic fatigue, or it might just be that some of the symptoms are common to both disorders. (Read more HERE.)

The differentiation of IH and fibromyalgia can also be challenging because of some similarity in symptoms. In particular, fatigue is also very common in people with fibromyalgia. However, in fibromyalgia there is also widespread pain, which is not a feature of IH, and so this differentiation is a little easier to make. Sleepiness, in contrast to fatigue, may not be a typical symptom of fibromyalgia and may indicate an underlying or additional sleep disorder.4

Many sleep disorders – insomnia, sleep apnea, circadian rhythm disorders, etc. – can cause fatigue, sleepiness, or both. It is very important that doctors assess for these sorts of sleep disorders before making a diagnosis of IH, chronic fatigue, or fibromyalgia. In some cases, the other sleep disorder causes all the symptoms, while in other cases, the other sleep disorder worsens the sleepiness or fatigue. Either way, treating the other (non-IH) sleep disorder can sometimes markedly improve symptoms.


  1. Maness, Caroline, et al. “Systemic Exertion Intolerance Disease/Chronic Fatigue Syndrome Is Common in Sleep Centre Patients with Hypersomnolence: A Retrospective Pilot Study.” Journal of Sleep Research, vol. 28, no. 3, 2018, doi:10.1111/jsr.12689.
  2. Stanford Center for Sleep Sciences and Medicine. “Is Fibromyalgia Syndrome a Myth? No, But It Just Might Be a Sleep Disorder.” HuffPost, HuffPost, 21 Apr. 2014.

Please help us continue this Ask the Doctor series by donating now, and if you have IH or a related sleep disorder, please join our registry at CoRDS now (or ensure your responses are updated).

Disclaimer for Ask the Doctor: The medical information provided is meant for educational purposes only and is not a substitute for professional medical care and advice. Each person is different, and questions about a personal health condition should be discussed with your own healthcare professional.

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