Chronic fatigue syndrome (
CFS), also called
myalgic encephalomyelitis (
ME) or
ME/CFS, is a complex, debilitating, long-term medical condition. The root cause(s) of the disease are unknown and the mechanisms are not fully understood. Distinguishing core symptoms are lengthy exacerbations or flare-ups of the illness following ordinary minor physical or mental activity, known as post-exertional malaise (PEM); greatly diminished capacity to accomplish tasks that were routine before the illness; and sleep disturbances. The Center for Disease Control and Prevention's (CDC) diagnostic criteria also require at least one of the following: (1) Orthostatic intolerance or (2) impaired memory or attention. Frequently and variably, other common symptoms occur involving numerous body systems, and chronic pain is very common. The often incapacitating fatigue in CFS is different from that caused by normal strenuous exertion, is not significantly relieved by rest, and is not due to a previous medical condition. Diagnosis is based on the person's symptoms because no confirmed diagnostic test is available.