What Is Chronic Fatigue Syndrome?

By Karen Lee Richards, ChronicPainConnection Lead Expert

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Chronic fatigue syndrome, also known as myalgic encephalopathy or ME/CFS, is an autoimmune illness characterized by profound and prolonged exhaustion that is not relieved by rest and is not directly caused by other illnesses or conditions. People who have chronic fatigue syndrome report flu-like symptoms that do not go away in a few days or even a few weeks. 

The Center for Disease Control (CDC) estimates that four million Americans have ME/CFS. However, because it is such a complicated illness, only about 20 percent of them have been diagnosed.


Although the primary symptom of ME/CFS is extreme fatigue, the International Chronic Fatigue Syndrome Study Group identified eight additional primary symptoms:

  • Loss of memory or concentration
  • Sore throat
  • Painful and mildly enlarged lymph nodes in neck or armpits
  • Unexplained muscle soreness
  • Pain that moves from one joint to another without swelling or redness
  • Headache of a new type, pattern or severity
  • Sleep disturbance
  • Extreme exhaustion after normal exercise

Another significant characteristic of chronic fatigue syndrome is “post-exertional malaise,” which is a period of deep exhaustion with a worsening of symptoms that follows physical exertion and that lasts for more than 24 hours.

Additional chronic fatigue syndrome symptoms that patients may experience include:

  • Abdominal pain
  • Alcohol intolerance
  • Bloating
  • Chest pain
  • Chronic cough
  • Depression, anxiety, panic attacks
  • Diarrhea
  • Dizziness
  • Dry eyes and mouth
  • Earache
  • Irregular heartbeat
  • Jaw pain
  • Morning stiffness
  • Nausea
  • Night sweats
  • Shortness of breath
  • Tingling sensations
  • Weight loss

The combination of symptoms for every ME/CFS patient is different, both in type and severity. Symptoms may wax and wane over time. While some patients eventually recover completely, others seem to get progressively worse.

Types of Chronic Fatigue Syndrome

There are two reported types of ME/CFS:

  1. Sudden onset: The majority of cases start suddenly, triggered by a flu-like virus, a severe infection, another illness, or a period of great physical or emotional stress.
  2. Gradual onset: Some cases begin with mild symptoms that slowly increase over time. Often gradual onset patients do not realize there is anything wrong for quite a while, and may attribute their symptoms to stress or other mild illnesses.


More information on Chronic Fatigue Syndrome 



“About CFIDS,” The CFIDS Association of America, Inc., 2004.

“Chronic Fatigue Syndrome,” MayoClinic.com, 2005.

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