Fatigue Chronic fatigue 2013-11-13T07:49:08Z HP:0012432 Chronic fatigue UMLS:C0518656 Chronic extreme exhaustion Note that chronic fatigue can be a symptom of chronic fatigue syndrome (CFS), which is characterized by profound fatigue that is not improved by bed rest and that may be worsened by physical or mental activity. Symptoms of CFS may include weakness, muscle pain, impaired memory, impaired mental concentration, and insomnia, which can result in reduced participation in daily activities. Subjective feeling of tiredness characterized by a lack of energy and motivation that persists for six months or longer.