Fatigue and high body temperature: what to know

Fatigue is a reduced sense of energy that can make ordinary activities feel harder. A raised temperature can happen when the immune system responds to infection or inflammation. COVID-19 is one possible cause, but fatigue and temperature changes can also occur with other infections, heat-related illness, dehydration, or an underlying health condition.

The reading can vary with the thermometer, time of day, recent exercise, warm surroundings, and medicines. Consider the whole pattern: chills, cough, sore throat, headache, vomiting, diarrhoea, pain, breathlessness, reduced urination, or a new rash can help a clinician decide what to check. Fatigue that continues after the temperature settles may need a separate assessment; possible contributors include anaemia, coeliac disease, burnout, chronic kidney disease, or chronic fatigue syndrome.

Rest, drink fluids regularly, and keep the room comfortably cool. Choose light meals if you can tolerate them, and avoid strenuous exercise and alcohol while you feel unwell. Check your temperature using the thermometer instructions and record the reading, time, symptoms, and any medicine taken.

Use fever or pain medicine only as directed on its label or by a clinician, and check with a pharmacist if you are pregnant, have kidney or liver disease, take other medicines, or are treating a child. Do not give aspirin to children or teenagers. Stay home from close contact when you have a fever or feel acutely unwell, and seek advice if symptoms are worsening or not improving.

Seek urgent medical help for trouble breathing, chest pain, confusion, fainting, a seizure, severe weakness, a stiff neck, a rapidly spreading rash, or inability to keep fluids down. Get prompt advice if you are passing very little urine, have signs of severe dehydration, or have a weakened immune system.

Arrange a medical review when the high temperature persists, returns after improving, or is accompanied by worsening pain, persistent vomiting, or fatigue that interferes with daily life. Infants, older adults, pregnant people, and people with long-term conditions may need earlier advice because illness can become serious more quickly.

Ask what might explain both symptoms, whether you need an examination or tests, how to monitor your temperature, and which warning signs should change your plan. Tell the clinician when symptoms began, your highest recorded reading, recent travel or sick contacts, fluid intake, medicines, and any long-term health conditions.