Fatigue describes a state of tiredness that does not resolve with rest or sleep. In general usage, fatigue is synonymous with extreme tiredness or exhaustion that normally follows prolonged physical or mental activity. When it does not resolve after rest or sleep, or occurs independently of physical or mental exertion, it may be a symptom of a medical condition that may become severe or progressive.Fatigue can be a feature of a mental disorder such as depression; may be associated with conditions of chronic pain such as fibromyalgia; it may also feature in conditions of chronic low-level inflammation, and be a disease-related symptom in many other conditions. Fatigue often has no known cause, and is recognised as being very complex in nature. Fatigability describes a susceptibility to fatigue.Physical fatigue results from muscle fatigue brought about by intense physical activity. Mental fatigue results from prolonged periods of cognitive activity which impairs cognitive ability. Mental fatigue can manifest as sleepiness, lethargy, or directed attention fatigue. Mental fatigue can also impair physical performance. Classification
Physical
Physical fatigue, or muscle fatigue, is the temporary physical inability of muscles to perform optimally. The onset of muscle fatigue during physical activity is gradual, and depends upon an individuals level of physical fitness – other factors include sleep deprivation and overall health. Physical fatigue can be caused by a lack of energy in the muscle, by a decrease of the efficiency of the neuromuscular junction or by a reduction of the drive originating from the central nervous system, and can be reversed by rest.
Management
Medications are reviewed as some have side effects that may contribute to fatigue and the interactions of medications are complex.Psychostimulants such as methylphenidate, amphetamines, and modafinil have been used in the treatment of fatigue related to depression, chronic fatigue syndrome, and medical illness such as cancer. They have also been used to counteract fatigue in sleep loss and in aviation. See also
References
Further reading
Byung-Chul Han: Müdigkeitsgesellschaft. Matthes & Seitz, Berlin 2010, ISBN 978-3882216165. (Philosophical essay about fatigue as a sociological problem and symptom). Danish edition: Træthedssamfundet. Møller, 2012, ISBN 978-8799404377. Dutch edition: De vermoeide samenleving. van gennep, 2012, ISBN 978-9461640710. Italian editions : La società della stanchezza. nottetempo, 2012, ISBN 978-8874523450. Korean edition: 한병철 지음 | 김태환 옮김. Moonji, 2011, ISBN 978-8932023960. Spanish edition: La sociedad del cansancio. Herder Editorial, 2012, ISBN 978-8425428685. External links

Fatigue –  Information for Patients, U.S. National Cancer Institute