Fever and fainting

Fever can increase fluid loss through sweating and reduce appetite or drinking. Standing suddenly while unwell may then lower blood pressure enough to cause light-headedness or a brief loss of consciousness. Dehydration is one possible explanation, not a diagnosis.

Other causes include low blood sugar, anaemia, abnormal heart rhythm, or a reflex response to pain. Atrial Fibrillation is one heart rhythm condition a clinician may consider when palpitations accompany an episode. Fainting does not establish the cause.

Lie flat with your legs raised if possible, and stay there until fully recovered. If someone has fainted, check breathing, protect them from injury, and do not give food or drink until alert and able to swallow. Rise slowly afterward.

Arrange medical advice after any unexplained faint, especially if it happened during exercise or with a new medicine. Record warning symptoms, recovery, injury, fever, fluid intake, and palpitations.

Call emergency services if the person does not wake promptly, is not breathing normally, has chest pain, severe breathlessness, a seizure, serious injury, new weakness, trouble speaking, or a sudden severe headache. Emergency assessment is also needed for fainting during exertion or with a very fast or irregular heartbeat.

Ask whether you need blood pressure checks, an electrocardiogram, blood tests, or assessment for infection. Discuss hydration, fever treatment, medicine effects, and whether to avoid driving until the cause is clear.