Symptom4 min read

Fatigue

Detail level

Fatigue is a feeling of weariness or lack of energy and differs from drowsiness. It has many causes, from poor sleep and stress to anaemia, diabetes and heart, kidney or liver disease, and should be checked if prolonged without explanation.

MedlinePlus defines fatigue as a feeling of exhaustion or lack of energy, and distinguishes it from drowsiness. Causes include anaemia, iron deficiency, thyroid disorders, diabetes and Addison's disease; depression and grief; sleep disorders such as insomnia and sleep apnoea; infections; cancer, heart failure, kidney and liver disease and malnutrition; certain medicines; and alcohol and drugs. NHS mentions lack of sleep, lifestyle, stress, hormonal changes and infections.

MedlinePlus suggests blood tests to look for anaemia, diabetes, inflammation and infection, as well as kidney, liver and thyroid function tests and a urine test. NHS advises seeing a doctor if tiredness lasts for weeks without a cause, interferes with daily life, or comes with other symptoms.

In one minute¹²³

What is it?: A feeling of exhaustion or lack of energy that differs from drowsiness.
Who is usually affected?: Common at all ages; it is linked to sleep, stress, diabetes, anaemia, and heart, kidney and liver disease.
Acute or chronic?: Temporary after lack of sleep, and persistent if an illness lies behind it.
Main symptoms: It may be accompanied by blurred vision or thirst in diabetes, or breathlessness in heart disease.
Red flags?: Yes: tiredness with confusion, dizziness, reduced urine output, swelling, or weight gain for no reason.
Preventable?: Enough sleep, balanced nutrition and regular exercise.

What is it?

Fatigue is a feeling of exhaustion, weariness or lack of energy. MedlinePlus distinguishes it from drowsiness: it is a lack of motivation, not merely a need for sleep.

NHS describes persistent, unexplained tiredness as something that may point to a medical problem needing attention.

Possible causes

According to MedlinePlus: anaemia and iron deficiency; thyroid disorders (underactive or overactive); diabetes; Addison's disease; depression and grief; insomnia, sleep apnoea and narcolepsy; infections (HIV, tuberculosis, hepatitis, mononucleosis, endocarditis, parasites, lupus); cancer, fibromyalgia, heart failure, kidney and liver disease, malnutrition, arthritis, COVID-19 and eating disorders; certain medicines (sedatives, antidepressants, antihistamines, blood pressure medicines, steroids, diuretics); and alcohol and drugs.

NHS mentions: lack of sleep and insomnia; an unhealthy lifestyle; stress, depression and bereavement; hormonal changes (puberty, pregnancy and the menopause); infections (glandular fever and COVID-19); and certain medicines and treatments.

How it is assessed

For unexplained fatigue, the doctor may request blood tests to look for anaemia, diabetes, inflammatory diseases and infection, tests of kidney, liver and thyroid function, and a urine test.

Self-care

According to MedlinePlus: enough sleep at night, balanced nutrition and hydration, regular exercise, relaxation techniques, reducing stress, and avoiding alcohol, nicotine, stimulants and sedatives. NHS advises keeping regular sleep times, avoiding screens for an hour before bed, and avoiding caffeine as well as food and exercise close to bedtime. No specific supplements are mentioned here.

When do you need urgent help?

Call emergency services now 998

Tiredness with suicidal thoughts: seek emergency help immediately or contact someone you trust to be with you now.¹

Get urgent care today

Tiredness with confusion, dizziness, blurred vision, reduced urine output, or unexplained swelling or weight gain: contact a doctor immediately.¹

See your doctor within days

Tiredness with no clear cause together with fever, sweating or weight loss, or lasting for weeks and disrupting daily life: book an appointment with a doctor.¹²

Educational content only — no diagnosis, and no substitute for a clinician.

Common questions

Does tiredness mean a vitamin deficiency?

It cannot be assumed. MedlinePlus lists many causes and advises a medical assessment; supplements are a matter to consider with a specialist.¹

When is fatigue linked to diabetes?

MedlinePlus lists diabetes among the causes of fatigue and mentions blood sugar testing as part of the assessment, and NIDDK and CDC count it among the common symptoms of diabetes.¹³⁴

Questions for your doctor

Which tests are right for me (blood, thyroid, kidney, sugar)?
Could my medicines be causing the fatigue?
Is my sleep adequate, and how do I assess it?
Do I need a psychological assessment?

References

1
MedlinePlus. Fatigue. medlineplus.gov/ency/article/003088.htm
Health agencies & guidelines · Accessed 2026-10-06
2
NHS. Tiredness and fatigue. www.nhs.uk/symptoms/tiredness-and-fatigue/
Health agencies & guidelines · Accessed 2026-10-06
3
NIDDK / NIH. Symptoms & Causes of Diabetes. www.niddk.nih.gov/health-information/diabetes/overview/symptoms-causes
Health agencies & guidelines · Accessed 2026-10-03
4
CDC. Symptoms of Diabetes. www.cdc.gov/diabetes/signs-symptoms/
Health agencies & guidelines · Accessed 2026-10-06

Review status: Edited content · Last updated: 2026-10-06

Change log

2026-10-06 — Page created.