Chronic fatigue syndrome (CFS), also called myalgic encephalomyelitis (ME) and ME/CFS, is a complex, fatiguing, long-term medical condition diagnosed by required primary symptoms and criteria, often involving a broad range of symptoms. Distinguishing core symptoms are lengthy exacerbations or "flares" of the illness after 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. [Source: Wikipedia 
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