Chronic fatigue syndrome is the common name for a group of significantly debilitating medical conditions characterized by persistent fatigue and other specific symptoms that lasts for a minimum of six months in adults. The fatigue is not due to exertion, not significantly relieved by rest, and is not caused by other medical conditions. CFS may also be referred to as myalgic encephalomyelitis, post-viral fatigue syndrome, chronic fatigue immune dysfunction syndrome, or by several other terms. Biological, genetic, infectious and psychological mechanisms have been proposed, but the etiology of CFS is not understood and it may have multiple causes. Symptoms of CFS include malaise after exertion; unrefreshing sleep, widespread muscle and joint pain, sore throat, headaches of a type not previously experienced, cognitive difficulties, chronic and severe mental and physical exhaustion, and other characteristic symptoms in a previously healthy and active person.