Chronic fatigue syndrome is a complicated illness. As its name states, it is a chronic condition, and it is characterized by a debilitating fatigue. The fatigue may be exacerbated by physical or mental exertion. Strangely enough, the fatigue is not alleviated by rest or relaxation [Mayo Clinic].
The cause of chronic fatigue syndrome is still unknown. The major symptom, the chronic fatigue, is also seen in such related conditions as myalgic encephalomyelitis (ME) and systemic exertion intolerance disease (SEID) [Mayo Clinic].