MedGen

Subjective feeling of tiredness characterized by a lack of energy and motivation that persists for six months or longer. [from HPO]

A syndrome of unknown etiology. Chronic fatigue syndrome (CFS) is a clinical diagnosis characterized by an unexplained persistent or relapsing chronic fatigue that is of at least six months'' duration, is not the result of ongoing exertion, is not substantially alleviated by rest, and results in substantial reduction of previous levels of occupational, educational, social, or personal activities. Common concurrent symptoms of at least six months duration include impairment of memory or concentration, diffuse pain, sore throat, tender lymph nodes, headaches of a new type, pattern, or severity, and nonrestorative sleep. The etiology of CFS may be viral or immunologic. Neurasthenia and fibromyalgia may represent related disorders. Also known as myalgic encephalomyelitis. [from NCI]