Chronic fatigue syndrome (CFS) is a long term and complex disease. It causes extreme fatigue that makes it hard for those who have it to get through the day. This means work and school can be difficult to do well. Rest doesn't make the fatigue better. CFS is sometimes known as systemic exertion intolerance disease (SEID).

Problems may exist for many months to years and range in severity. Some people get better over time, while others continue to get worse. Most will have a cycle of improvement and flare ups.

CFS is very hard to diagnose. It may take some time before a diagnosis of CFS is made. The cause of CFS is not known. The most common theory is that CFS is set off by an infection or other immune system problems.

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Revision Information

  • Reviewer: EBSCO Medical Review Board Marcin Chwistek, MD
  • Review Date: 12/2018 -
  • Update Date: 02/08/2019 -