What causes fatigue?

Insomnia can leave you unrefreshed even after time in bed. Influenza and glandular fever often bring fatigue with fever, aches, sore throat, or swollen glands. Hypothyroidism may cause low energy with feeling cold, constipation, dry skin, or slowed thinking. Anaemia can be associated with breathlessness, paleness, dizziness, or heavy bleeding. Fatigue with swelling, breathlessness when lying down, or reduced exercise tolerance needs assessment for heart failure. Hepatitis B, hepatitis C, and HIV infection may cause fatigue with other signs, or sometimes few early symptoms.

Consider whether the tiredness is sleepiness, physical weakness, reduced motivation, or breathlessness; these distinctions help guide the assessment.

Keep regular sleep and waking times, eat consistent nourishing meals, drink enough fluid, and pace activity with rest. Review recent illness, mood, sleep quality, and medicines with a clinician if fatigue lasts, limits work or daily tasks, or keeps returning. A clinician may examine you and choose blood tests based on your symptoms rather than testing every possible cause.

Seek urgent help for fatigue with chest pain, severe breathlessness, fainting, new confusion, one-sided weakness, black or bloody stools, or rapidly worsening illness. Arrange prompt review for unexplained weight change, persistent fever, yellow skin or eyes, or fatigue that is progressively limiting normal activities.

Could sleep, mood, medicines, anaemia, thyroid function, infection, or another condition explain this? Which symptoms should I monitor? What tests are appropriate for my pattern of fatigue?