What does fatigue mean in a medical context?

Reviewed by Yoshinori Abe, MD

Internal Medicine

Fatigue is a persistent feeling of physical and mental tiredness or exhaustion that goes beyond normal sleepiness. It can make everyday activities—like working, exercising, or concentrating—feel difficult or overwhelming. Unlike ordinary tiredness that improves with rest, medical fatigue often lingers and may signal an underlying health condition, such as anemia, thyroid issues, sleep disorders, depression, or chronic illness.

Because fatigue has so many possible causes, identifying the root issue is essential to feeling better. Rather than guessing, take a free, instant, online symptom check to explore what could be behind your exhaustion and get personalized guidance on next steps. It only takes a few minutes and can help you have a more informed conversation with your doctor.

Reviewed for medical accuracy: 07/14/2026

Important Next Steps

Learn what could be causing fatigue Discover if your fatigue needs care Find out if fatigue is serious See OTC options for fatigue relief Find a doctor for fatigue symptoms Understand medically valid fatigue home remedies Check likely causes of your fatigue

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Explanation

Fatigue in the medical world means feeling very tired and not having enough energy to do things. It can be caused by many things, like not getting enough sleep, working too hard, or being sick.

Types of Fatigue

Physical Fatigue: This is when your body feels tired. You might feel like your muscles are weak and you can't do things you usually do, like playing or running.
Mental Fatigue: This is when your mind feels tired. It might be hard to think clearly, pay attention, or remember things.

Causes of Fatigue

Lack of Sleep: Not sleeping enough can make you feel tired all the time.
Illness: Being sick, like having a cold or the flu, can make you feel worn out.
Stress: Feeling worried or stressed can also make you feel very tired.

Fatigue is different from just being sleepy. Sleepiness is when you feel like you want to go to sleep, but fatigue is when you feel like you can't do things even if you're not sleepy. If you feel very tired for a long time, it's important to use a free symptom checker to help identify what might be causing your fatigue and determine if you should see a doctor.

(References)

Evans WJ, & Lambert CP. (2007). Physiological basis of fatigue. American journal of physical medicine & rehabilitation, 17370370.
Shen J, Barbera J, & Shapiro CM. (2006). Distinguishing sleepiness and fatigue: focus on definition .... Sleep medicine reviews, 16376590.
Jason LA, Evans M, Brown M, & Porter N. (2010). What is fatigue? Pathological and nonpathological fatigue. PM & R : the journal of injury, function, and rehabilitation, 20656613.

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