Symptom · Whole body
Fatigue
Also known as: tiredness, exhaustion, lack of energy
Persistent tiredness that rest does not fix. It is one of the commonest reasons to see a doctor and usually reflects sleep, mood, workload or lifestyle rather than disease, but it is also the presenting feature of anaemia, thyroid disease, diabetes, infections and heart, lung, liver and kidney conditions.
What it is
Persistent tiredness that rest does not fix. It is one of the commonest reasons to see a doctor and usually reflects sleep, mood, workload or lifestyle rather than disease, but it is also the presenting feature of anaemia, thyroid disease, diabetes, infections and heart, lung, liver and kidney conditions.
Common causes
Poor or short sleepIncluding shift work, insomnia and obstructive sleep apnoea (snoring, unrefreshing sleep, daytime dozing).
Depression and anxietyLow mood, loss of interest, early waking and poor concentration.
AnaemiaEspecially iron deficiency in menstruating women and people with poor diet or bleeding.
Underactive thyroidWeight gain, feeling cold, constipation and dry skin.
Viral infections and their aftermathGlandular fever, flu, COVID-19 and other infections can leave weeks of fatigue.
LifestyleAlcohol, inactivity, excess caffeine, crash dieting.
Less common causes
DiabetesWith thirst, frequent urination and weight loss.
Heart failure, COPD, kidney and liver diseaseFatigue with breathlessness, swelling or jaundice.
Coeliac disease and inflammatory bowel diseaseFatigue with bowel symptoms and weight loss.
Chronic fatigue syndrome / MEDisabling fatigue over six months, worsened by exertion, diagnosed after excluding other causes.
CancerWith weight loss, night sweats or a lump.
Medication side effectsBeta blockers, antihistamines, opioids, antidepressants.
Often occurs with
Seek urgent care if
- Fatigue with chest pain, breathlessness at rest or fainting
- Fatigue with unexplained weight loss, night sweats, persistent fever or bleeding
- Thoughts of self-harm alongside exhaustion and low mood
Conditions to read about
AnaemiaUnderactive thyroid (hypothyroidism)Type 2 diabetesHeart failureChronic kidney diseaseCirrhosis
How it is investigated
Full blood countThyroid function testsBlood glucoseKidney function testsLiver function testsCRP test
Educational content. This page explains what a symptom can mean so that the anatomy and the medical reasoning make sense. It cannot tell you what is causing yours: only a clinician who can examine you and order tests can do that.