General
Fatigue
A persistent lack of energy or overwhelming tiredness that is not relieved by rest and interferes with normal life — usually explained by lifestyle, low mood or sleep, but sometimes the first sign of anaemia, an underactive thyroid, diabetes or another underlying condition.
Education and reference only. This explains the common causes of fatigue and the warning signs that need urgent help, in plain language — it is not a diagnosis or a substitute for advice from a clinician. If you feel very unwell or are worried, seek medical help.
Quick answer
What is fatigue?
Everyone feels tired sometimes, but fatigue is more than ordinary tiredness: it is a deep, persistent lack of physical or mental energy that sleep does not fully restore and that affects how a person functions. It is one of the commonest reasons people see a doctor, and the cause is frequently a combination of factors rather than a single disease — poor or disrupted sleep, stress, low mood, doing too much, alcohol and inactivity all drain energy.
- Get urgent help: Seek urgent help if fatigue comes with chest pain, severe breathlessness or fainting — this needs assessment the same day. See a doctor promptly if fatigue comes with unexplained weight loss, drenching night sweats or unusual lumps.
- Self-care: Much fatigue improves with attention to the basics of healthy living.
About fatigue
Everyone feels tired sometimes, but fatigue is more than ordinary tiredness: it is a deep, persistent lack of physical or mental energy that sleep does not fully restore and that affects how a person functions. It is one of the commonest reasons people see a doctor, and the cause is frequently a combination of factors rather than a single disease — poor or disrupted sleep, stress, low mood, doing too much, alcohol and inactivity all drain energy. When fatigue is persistent or unexplained, however, it can point to a physical cause such as anaemia, an underactive thyroid gland, poorly controlled blood sugar, a vitamin deficiency or a lingering viral illness. The pattern matters: fatigue that has appeared recently, is worsening, or comes with other symptoms such as weight loss, breathlessness, fever or unusual bleeding deserves investigation, whereas long-standing tiredness with a clear lifestyle explanation may improve with simple changes.
When to get help
Call 999 or go to A&E if fatigue comes with any of these warning signs:
- Seek urgent help if fatigue comes with chest pain, severe breathlessness or fainting — this needs assessment the same day.
- See a doctor promptly if fatigue comes with unexplained weight loss, drenching night sweats or unusual lumps.
- See a doctor promptly if you are unusually pale, breathless, or bruising or bleeding easily alongside the tiredness.
- Seek prompt help if tiredness is severe, came on quickly, and you also feel very thirsty and are passing lots of urine.
- Seek help promptly if fatigue is paired with low mood and thoughts of not wanting to go on — you do not have to cope alone.
When to see a doctor
See a doctor if fatigue lasts more than a few weeks despite better sleep and lifestyle, if it is getting steadily worse, or if it comes with other symptoms such as weight loss, breathlessness, fever, night sweats, unusual bleeding or marked thirst. A simple set of blood tests can identify common causes such as anaemia, thyroid problems, diabetes or vitamin deficiency. Seek help sooner if the tiredness is severe and disabling, or if it is bound up with low mood and you are struggling to cope, as support is available and effective.
Not sure how urgent it is? It is always OK to call NHS 111 for advice, day or night.
What can cause it
Common causes of fatigue
Fatigue has many possible causes. Each links to a full, plain-language guide to that condition — what it is, how it's treated and when to seek help.
What helps
Self-care and what you can do
Much fatigue improves with attention to the basics of healthy living. Aim for a regular sleep routine with a consistent bedtime and wake time, limit screens and caffeine in the evening, and keep the bedroom dark and quiet. Eat regular, balanced meals to keep your energy steady, stay hydrated, and build up gentle, regular activity — exercise paradoxically tends to increase energy over time. Cut back on alcohol, which fragments sleep, and try to ease pressure where you can, since stress and low mood are powerful drains on energy. Pacing your day, taking short breaks and tackling demanding tasks when you feel freshest can all help while you address the underlying cause.
Answers
Fatigue: frequently asked questions
How long should I wait before seeing a doctor about tiredness?
If genuine fatigue lasts more than two to four weeks despite improving your sleep, diet and activity, it is worth a routine appointment and some basic blood tests to look for causes such as anaemia, thyroid problems or low vitamin D.
What blood tests are usually done for fatigue?
A clinician will often check for anaemia, thyroid function, blood sugar, kidney and liver function and sometimes vitamin levels. The exact tests depend on your other symptoms and history.
Can low mood and stress really cause physical tiredness?
Yes. Depression, anxiety and chronic stress are among the most common causes of persistent fatigue, and they often disturb sleep, which adds to the tiredness. Addressing mental health is an important part of tackling fatigue.
Why am I still tired even though I sleep plenty?
Unrefreshing sleep can come from poor sleep quality, an underlying condition such as anaemia or thyroid trouble, or low mood. If good-quality, sufficient sleep still leaves you exhausted, it is worth being assessed.
Sources
Where this is drawn from
- NICE CKS: Tiredness/fatigue in adults.
- British Thyroid Foundation: hypothyroidism and tiredness.
Related symptoms
Tell us what you need. We'll route it to the right expert.
Request a proposal, book a scoping call, or speak to our team directly.