Chronic fatigue syndrome

In medicine, chronic fatigue syndrome is "a syndrome characterized by persistent or recurrent fatigue, diffuse musculoskeletal pain, sleep disturbances, and subjective cognitive impairment of 6 months duration or longer. Symptoms are not caused by ongoing exertion; are not relieved by rest; and result in a substantial reduction of previous levels of occupational, educational, social, or personal activities. Minor alterations of immune, neuroendocrine, and autonomic function may be associated with this syndrome. There is also considerable overlap between this condition and fibromyalgia."

Etiology
Xenotropic murine leukemia virus-related virus (XMRV), a human gammaretrovirus, may contribute to infection. In one study, the virus was found "in nearly 98 percent of about 300 patients with the syndrome" while only 3.7 percent of 218 healthy people were infected.