Fatigue

==== Primary vs. secondary ====
In some areas it has been proposed that fatigue be separated into primary fatigue, caused directly by a disease process, and ordinary or secondary fatigue, caused by a range of causes including exertion and also secondary impacts on a person of having a disease (such as disrupted sleep).<ref>{{Cite web|url=https://practicalneurology.com/articles/2018-july-aug/fatigue-in-patients-with-multiple-sclerosis|title=Fatigue in Patients with Multiple Sclerosis|access-date=2021-10-18|archive-date=2022-06-16|archive-url=https://web.archive.org/web/20220616230104/https://practicalneurology.com/articles/2018-july-aug/fatigue-in-patients-with-multiple-sclerosis|url-status=live}}</ref><ref>{{cite journal | vauthors = Chalah MA, Riachi N, Ahdab R, Créange A, Lefaucheur JP, Ayache SS | title = Fatigue in Multiple Sclerosis: Neural Correlates and the Role of Non-Invasive Brain Stimulation | journal = Frontiers in Cellular Neuroscience | volume = 9 | page = 460 | year = 2015 | pmid = 26648845 | pmc = 4663273 | doi = 10.3389/fncel.2015.00460 | doi-access = free }}</ref><ref name="Gerber et al 2019">{{cite journal | vauthors = Gerber LH, Weinstein AA, Mehta R, Younossi ZM | title = Importance of fatigue and its measurement in chronic liver disease | journal = World Journal of Gastroenterology | volume = 25 | issue = 28 | pages = 3669–3683 | date = July 2019 | pmid = 31391765 | pmc = 6676553 | doi = 10.3748/wjg.v25.i28.3669 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Hartvig Honoré P |title=Fatigue |journal=European Journal of Hospital Pharmacy |date=June 2013 |volume=20 |issue=3 |pages=147–148 |doi=10.1136/ejhpharm-2013-000309 |s2cid=220171226 |doi-access=free }}</ref><ref>{{Cite journal|title=Central fatigue in multiple sclerosis: a review of the literature: The Journal of Spinal Cord Medicine: Vol 39, No 4|date=2016 |doi=10.1080/10790268.2016.1168587 |pmid=27146427 |pmc=5102292 |journal=The Journal of Spinal Cord Medicine |volume=39 |issue=4 |pages=386–399 | vauthors = Newland P, Starkweather A, Sorenson M }}</ref><ref>{{cite journal |last1=Patejdl |first1=Robert |last2=Zettl |first2=Uwe K. |title=The pathophysiology of motor fatigue and fatigability in multiple sclerosis |journal=Frontiers in Neurology |date=27 July 2022 |volume=13 |doi=10.3389/fneur.2022.891415 |doi-access=free |pmid=35968278 |pmc=9363784 }}</ref> The ICD-11 MG22 definition of fatigue<ref>{{Cite web|url=https://icd.who.int/browse11/l-m/en#/http://id.who.int/icd/entity/1109546957|title=ICD-11 for Mortality and Morbidity Statistics|website=icd.who.int|access-date=2021-11-26|archive-date=2018-08-01|archive-url=https://archive.today/20180801205234/https://icd.who.int/browse11/l-m/en%23/http://id.who.int/icd/entity/294762853#/http://id.who.int/icd/entity/1109546957|url-status=live}}</ref> captures both types of fatigue; it includes fatigue that "occur[s] in the absence of... exertion... as a symptom of health conditions."{{medical citation needed|date=March 2024}}