Sudden debilitating fatigue of unknown cause. It may follow a nonspecific illness with mild fever, tender lymph nodes, sore throat, headaches, weakness, muscle and joint pain, and confusion or difficulty in concentrating. To meet the criteria of CFS, the syndrome must be new, with a definite point of onset, and must persist more than six months. Once dismissed as imaginary, CFS remains controversial. Many authorities question whether it is a distinct disorder, since there is considerable overlap with other conditions such as fibromyalgia and Gulf War syndrome. No diagnostic test for CFS exists. Although a number of theories about the cause of CFS have been advanced, none has been proved. No cure has been found, but most patients improve gradually.

Learn more about chronic fatigue syndrome (CFS) with a free trial on Britannica.com.

Chronic may refer to:

• Chronic (medical) a persistent and lasting disease or medical condition, or one that has developed slowly
• Chronic toxicity,
• The Chronic, a 1992 album by Dr. Dre
• 2001 (album), a 1999 album by Dr. Dre originally to be called The Chronic 2001
• Slang for bad, extremely unpleasant
• A slang term in North America for Cannabis (Marijuana, Weed) of "better-than-average" quality.

See also

• Chronos