Key Takeaways
  • Chronic fatigue syndrome is marked by long-term fatigue, malaise or discomfort, and unrefreshing sleep.
  • Daytime symptoms can affect an individual’s work, school, or athletic performance, as well as personal relationships.
  • Symptoms are often confused for similar conditions that cause excessive sleepiness and can be misdiagnosed.

Chronic fatigue syndrome is a long-term disease that causes significant fatigue, often accompanied by sleep problems, trouble concentrating, and physical symptoms. Otherwise known as myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), it is a rare disorder that affects an estimated two million people in the U.S. and between 0.1% and 0.5% of people worldwide.

ME/CFS classified as a nervous system disorder thought to involve the neurological, endocrine, and immune systems. However, researchers do not fully understand the physical causes of ME/CFS, so they are not sure how to best treat it. Diagnosing ME/CFS can be difficult because the symptoms are often similar to those seen in other medical conditions.

Primary Symptoms

According to the National Academy of Medicine (NAM), the three primary ME/CFS symptoms are:

  • Fatigue: Feeling unusually tired for no apparent reason, even when the person is well-rested or has not done anything tiring, that affects the ability to practice activities that they used to enjoy. After performing activities that require physical effort, fatigue and discomfort often linger for more than a day.
  • Post-Exertional Malaise (PEM): Discomfort from ME/CFS increases after physical or mental effort. Because this is a key symptom of ME/CFS, some researchers have proposed renaming the condition “systemic exertion intolerance disease” (SEID) .
  • Unrefreshing Sleep: Continuing to feel tired even after obtaining sufficient sleep.

To qualify as ME/CFS, symptoms cannot be fully explained by another disorder Also, all three ME/CFS symptoms must be present for more than six months, and be at a moderate to severe level for at least 50% of the time. In addition to the primary symptoms, the person must either experience worsening symptoms after standing or sitting upright, or memory and concentration difficulties, also called “brain fog,” that become more severe when the person is tired, stressed, or under time pressure.

The disorder often occurs in people who previously led physically active lifestyles and often starts with an instance of immune system dysfunction that becomes chronic. ME/CFS tends to have a clearly marked onset, frequently following an injury, accident, or illness, such as COVID-19. It currently appears to be more common in women and those between 40 and 60 years old.

Other Common Symptoms

Along with fatigue, people with ME/CFS might report other symptoms including:

  • Breathing changes
  • Heart palpitations
  • Dizziness after standing
  • Slow digestion
  • Bowel and bladder dysfunction
  • Headaches
  • Concentration or memory issues
  • Insomnia, or difficulty staying asleep at night
  • Hypersomnia, or the need to sleep during the day
  • Nausea and vomiting
  • Night sweats
  • Low tolerance for alcohol or medications
  • Anxiety and depression
  • Painful lymph nodes
  • Sore throat
  • Muscle pain, which is more common in children and may be a sign that the person also has a coexisting condition

ME/CFS may affect someone’s ability to work, study, socialize, or enjoy hobbies, especially if they experience anxiety or panic attacks due to their symptoms.

Chronic Fatigue Syndrome and Similar Disorders

ME/CFS encompasses a wide range of symptoms that affect most systems in the body, so doctors may easily confuse it for another disorder. Examples of the many conditions that may cause similar symptoms include anemia, diabetes, cancer, celiac disease, and several sleep disorders.


Narcolepsy is marked by sudden, unexpected urges to sleep during the day . In contrast to ME/CFS, in which fatigue is made worse by activity, narcolepsy sleep attacks occur more frequently during monotonous activities. Another difference is that people with narcolepsy tend to feel refreshed after sleep, whereas people with ME/CFS experience unrefreshing sleep. Most people with narcolepsy also have cataplexy, or a sudden loss of muscle tone that often occurs in response to strong emotions such as laughter, not normally experienced by people with ME/CFS.

Excessive Sleepiness

Multiple sleep disorders and other health disorders can cause excessive sleepiness, but when the cause is not known, a person may be diagnosed with idiopathic hypersomnia. People with hypersomnia often sleep for 10 to 12 hours a day. They may feel groggy for a long time after waking up in the morning, or they may take long naps and wake up feeling unrefreshed. However, hypersomnia causes sleepiness rather than fatigue, and people with hypersomnia tend to fall asleep unusually quickly, which is not a typical trait of ME/CFS.


Fibromyalgia may present very similarly to ME/CFS. Fibromyalgia primarily causes undefined pain in various parts of the body, but it can also cause fatigue and cognitive issues similar to those seen in ME/CFS. Other autoimmune disorders, like lupus or rheumatoid arthritis, may also appear similar. Doctors may need to test for antibodies to rule out these disorders.


Depression and other mental health disorders, such as bipolar disorder or schizophrenia, may look similar to ME/CFS. Older adults experiencing depression may be especially likely to have unrefreshing sleep, fatigue, and brain fog. The two disorders may share similar pathways and, for some people, may coexist . Compared with depression, ME/CFS is more likely to cause extreme fatigue after doing something that requires minimal effort.

Obstructive Sleep Apnea

People with obstructive sleep apnea (OSA) experience a blocked or partially blocked airway, causing them to fully or completely stop breathing multiple times per night. These lapses in breathing disturb sleep, even if the person is unaware of them, leading to daytime sleepiness. To differentiate ME/CFS from OSA, doctors can conduct a sleep study or ask a bed partner if they have noticed their companion snoring, gasping, choking, or pausing their breathing during sleep.

How Is Chronic Fatigue Syndrome Diagnosed?

There is no specific test that conclusively proves the existence of ME/CFS Instead, a doctor examines a person and rules out other possible conditions through physical tests and other analyses.

A commonly used guide from the Institute of Medicine requires a person to display the three primary symptoms for at least six months to be diagnosed with ME/CFS:

  • Disruptive fatigue that does not resolve after resting
  • PEM or worsened fatigue after performing usual activities
  • Unrefreshing sleep

Symptoms can come and go, and they vary from person to person. This variability can make it difficult for diagnostic measures to capture how a person is affected by the disease, even if the effects are real and noticeable. Some experts argue that ME/CFS should be further divided into different subtypes based on groups of symptoms.

Talking with Your Healthcare Provider

Since ME/CFS can be difficult to diagnose, it is helpful to come prepared to your doctor’s appointment. Think back to when your symptoms first started, and whether they may be linked to a stressful event or an illness. Make a note of all the symptoms you have experienced, even if they do not seem directly related to ME/CFS. This can help your doctor rule out other conditions.

You may also want to prepare a list of questions to ask your doctor. Treatment for ME/CFS tends to focus on managing symptoms through medication, therapy, and lifestyle changes. Tell your doctor about your preferences regarding activity levels, so they can help establish a treatment plan that works for you. They may need to refer you to specialists for more targeted treatment of certain symptoms.

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6 Sources

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