As reported from the Centers for Disease Control and Prevention, The National Institutes of Health, and the International Chronic Fatigue Syndrome Study Group in the Annals of Internal Medicine, Volume 121, Number 12, December 15, 1994, page 956, "The Chronic Fatigue Syndrome: A Comprehensive Approach to Its Definition and Study."

"A case of the chronic fatigue syndrome is defined by the presence of the following: 1) clinically evaluated, unexplained, persistent or relapsing chronic fatigue that is of a new or definite onset (has not been lifelong); is not the result of ongoing exertion; is not substantially alleviated by rest; and results in substantial reduction in previous levels of occupational, educational, social or personal activities; and, 2) the concurrent occurrence of four or more of the following symptoms, all of which must have persisted or recurred during six or more consecutive months of illness and must have not predated the fatigue; self-reported impairment in short-term memory or concentration severe enough to cause substantial reduction in previous levels of occupational, educational, social, or personal activities; sore throat; tender cervical or auxiliary lymph nodes; muscle pain, multijoint pain without joint swelling or redness; headaches of a new type, pattern, or severity; unrefreshing sleep; and post-exertional malaise lasting more than 24 hours."