Fatigue

===Characteristics by cause===
Differentiating characteristics of fatigue that may help identify the possible cause of fatigue include
* [[Post-exertional malaise]]; a common feature of ME/CFS fatigue,<ref>{{Cite web |url=https://www.iqwig.de/download/n21-01_me-cfs-aktueller-kenntnisstand_abschlussbericht_v1-0.pdf |title=Myalgische Enzephalomyelitis / Chronic Fatigue Syndrome (ME/CFS) – Aktueller Kenntnisstand |access-date=2024-03-26 |archive-date=2023-11-02 |archive-url=https://web.archive.org/web/20231102160213/https://www.iqwig.de/download/n21-01_me-cfs-aktueller-kenntnisstand_abschlussbericht_v1-0.pdf |url-status=live }}</ref> but not a feature of other fatigues. 
* Increased by heat or cold; [[Signs and symptoms of multiple sclerosis#Fatigue|MS fatigue]] is in many cases effected in this way.<ref>{{Cite web|url=https://mstrust.org.uk/a-z/temperature-sensitivity|title=Temperature sensitivity &#124; MS Trust|first=M. S.|last=Trust|website=mstrust.org.uk}}</ref><ref>{{Cite web|url=https://www.msaustralia.org.au/news/ms-and-heat-fatigue/|title=MS and heat fatigue: does it come down to sweating?}}</ref> 
* Remission; MS fatigue may reduce during periods of other MS symptom remission.<ref>{{Cite web|url=https://practicalneurology.com/articles/2018-july-aug/fatigue-in-patients-with-multiple-sclerosis|title=Fatigue in Patients With Multiple Sclerosis|website=Practical Neurology}}</ref><ref>https://www.mssociety.org.uk/about-ms/types-of-ms/relapsing-remitting-ms.</ref> ME/CFS may also have lower periods of activity.<ref name="auto3">{{Cite web|url=https://www.cdc.gov/me-cfs/healthcare-providers/presentation-clinical-course/index.html|title=Presentation and Clinical Course of ME/CFS &#124; Information for Healthcare Providers &#124; Myalgic Encephalomyelitis/Chronic Fatigue Syndrome ME/CFS &#124; CDC|date=November 19, 2019|website=www.cdc.gov}}</ref>
* Cognitive declines; [[sleep deprivation]] causes cognitive and neurobehavioral effects including unstable attention and slowing of response times.<ref>
A 2009 review found that sleep loss had a wide range of cognitive and neurobehavioral effects including unstable attention, slowing of response times, decline of memory performance, reduced learning of cognitive tasks, deterioration of performance in tasks requiring divergent thinking, perseveration with ineffective solutions, performance deterioration as task duration increases; and growing neglect of activities judged to be nonessential. Table 1. {{Cite journal|title=Neurocognitive Consequences of Sleep Deprivation - PMC|date=2009 |pmc=3564638 |journal=Seminars in Neurology |volume=29 |issue=4 |pages=320–339 |doi=10.1055/s-0029-1237117 |pmid=19742409 | vauthors = Goel N, Rao H, Durmer JS, Dinges DF }}</ref>
* Intermittency; Fatigues often vary in how and when they occur. For instance ME/CFS symptoms can fluctuate during the day, from day to day, and over longer periods.<ref name="auto3"/> However some fatigues (RA, cancer fatigue<ref>{{Cite web|url=https://www.cancerresearchuk.org/about-cancer/coping/physically/fatigue/what-is-cancer-fatigue|title=What is cancer fatigue?|website=www.cancerresearchuk.org}}</ref>) seem to often be continual (24/7) whilst others (MS, Sjögren's, lupus, brain injury<ref>{{Cite web|url=https://www.brainline.org/article/fatigue-after-brain-injury-brainline-talks-dr-nathan-zasler|title=Fatigue After Brain Injury: BrainLine Talks With Dr. Nathan Zasler &#124; BrainLine|date=February 4, 2010|website=www.brainline.org}}</ref>) are often intermittent.<ref name="auto"/> A 2010 study found that Sjögren's patients reported fatigue after rising, an improvement in mid-morning, and worsening later in the day, whereas lupus (SLE) patients reported lower fatigue after rising followed by increasing fatigue through the day.<ref name="auto1">{{cite journal |last1=Ng |first1=W. F. |last2=Bowman |first2=S. J. |title=Primary Sjogren's syndrome: too dry and too tired |journal=Rheumatology |date=May 2010 |volume=49 |issue=5 |pages=844–853 |doi=10.1093/rheumatology/keq009 |pmid=20147445 }}</ref> The pace of onset may be a related differentiating factor; MS fatigue can have abrupt onset.<ref>{{cite web | url=https://mstrust.org.uk/a-z/fatigue | title=Fatigue &#124; MS Trust }}</ref>

Some people may have multiple causes of fatigue.