After treatment and remission

Chronic fatigue

For some people tiredness continues for months or even years after treatment ends. This topic explains how treatable causes of long-lasting fatigue are looked for and how to manage energy in daily life.

Last updated: 14 October 2026~3 min read

Warm light slowly rising upward. — **Figure 1.**Energy refills slowly.

01Short answer

Cancer-related fatigue is different from ordinary tiredness: it does not go away with rest and sleep and gets in the way of daily life. It is common for fatigue to last through the first months after treatment (topic “Why tiredness lingers”). But when it lasts months or years it is called chronic fatigue, and it is important to look for causes. Treatable causes include anaemia, an underactive thyroid (topic “Thyroid”), other hormone problems (topic “Hormones”), late effects on the heart or lungs, sleep problems, depression and anxiety, pain, medicine side effects, nutrition and loss of fitness. The doctor checks for these with blood tests and an examination. The best-proven help is physical activity that is increased gradually. Pacing (spreading energy through the day), a regular sleep routine, psychological support (such as cognitive behavioural therapy) and rehabilitation programmes also help.

02Simple explanation

Cancer-related fatigue does not go away with rest.

If it lasts months, the cause is looked for.

Causes: anaemia, thyroid, heart, sleep, mood.

Most helpful: gradually increasing activity.

Also: pacing, sleep, psychological support.

03Scientific explanation

Definition: according to the NCI, cancer-related fatigue is persistent tiredness out of proportion to activity, not relieved by rest and interfering with daily life; in some survivors it lasts for years.

Checking causes: ASCO and the NCI recommend checking for anaemia, thyroid function, sleep, pain, depression, medicines and late effects on organs.

Physical activity: according to the ACS and CRUK, regular, gradually increasing activity is the approach with the strongest evidence for reducing fatigue.

Psychological approaches: the NCI notes that cognitive behavioural therapy and mindfulness programmes can reduce fatigue.

04What happens in the body?

How is it different from ordinary tiredness?

It does not lift even after sleep and rest, it feels like heaviness in body and mind, and interest in things you enjoy drops.

Why does it continue?

Often several causes act together: hormones, blood, sleep, mood, pain and loss of fitness.

Coloured threads of light meeting in one knot. — **Figure 2.**Fatigue often has several causes.

What does the doctor check?

Blood tests (anaemia, thyroid, kidneys and liver, sugar), heart and lung tests if needed, sleep and mood questionnaires, and a review of your medicines.

How can I manage my energy?

Keep an energy diary, put important tasks at your most energetic times, break tasks into parts and take short rests in between — this is called pacing.

Glowing stones across calm water. — **Figure 3.**Alternate activity and rest.

Movement, sleep and support

Start with light activity such as walking and build up gradually. Go to bed and get up at the same time, and avoid long daytime naps. A psychologist and a rehabilitation specialist can help.

When to call your doctor

Worrying signs — fever, bleeding, new pain, breathlessness — should be reported to your doctor between visits too. Getting in touch early is always better than waiting.

05Managing fatigue

Steps.

1TrackKeep an energy diary.

2CausesAnaemia, thyroid, heart, sleep, mood.

3MoveGradually increasing activity.

4SleepA regular sleep routine.

EnergyEnergy builds gradually.

ActivityMoving gets easier.

SleepSleep improves.

06Causes of chronic fatigue (simplified)

Cause	How it is checked	What is done
Anaemia	Blood test	Treatment of the cause
Thyroid/hormones	TSH, T4, hormones	Hormone treatment
Sleep problems	Questionnaire, sleep study	Sleep routine, treatment
Depression, anxiety	Questionnaire, conversation	Psychological support
Loss of fitness	Examination	Gradual activity

* Your doctor checks for causes.

07Key terms

Chronic fatigue: Tiredness lasting for months.
Pacing: Spreading energy through the day.
Anaemia: Too few red blood cells.
Cognitive behavioural therapy: A talking therapy that works with thoughts and habits.
Rehabilitation: A programme to rebuild strength and activity.
Energy diary: A record of energy levels through the day.

08Key points

Fatigue is real and common.
Get the causes checked.
Move gradually.
Spread out your energy.
Keep a sleep routine.
Accept psychological support.

09Frequently asked questions

Will it go away if I sleep more?

Usually not; too much sleep can sometimes increase fatigue. A regular routine helps more.

Should I exercise if I feel tired?

Yes, lightly and gradually; avoid heavy exertion and check with your doctor.

Will vitamins help?

Usually not unless you have a deficiency; do not take them without your doctor’s advice.

Can I go back to work?

Often yes, step by step; discuss adjustments with your employer.

Does this information replace medical advice?

No. This is general education; only your treating doctor can assess your situation.

10Questions for your doctor

Take these questions to your appointment. The ones you save are collected on the “My questions” page and stay on this device only.

Will it go away if I sleep more?
Should I exercise if I feel tired?
Will vitamins help?
Can I go back to work?
Does this information replace medical advice?

My questions

12Sources

National Cancer Institute. Fatigue (PDQ®)
American Cancer Society. Cancer-related Fatigue
Cancer.Net (ASCO). Fatigue
Cancer Research UK. Fatigue and cancer
MedlinePlus (U.S. National Library of Medicine). Fatigue
Children's Oncology Group. Long-Term Follow-Up Guidelines for Survivors of Childhood, Adolescent and Young Adult Cancers
National Cancer Institute (NCI). Follow-Up Medical Care
National Cancer Institute (NCI). Cancer Survivorship
Cancer.Net (ASCO). Follow-Up Care After Cancer Treatment
Leukemia & Lymphoma Society (LLS). Long-Term and Late Effects of Treatment

Medical disclaimerThis information is for educational purposes only and does not replace medical advice.

Last updated: 14 October 2026← Back to the list

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