Fainting with the flu: what to know

Flu can reduce your fluid intake while fever and sweating increase fluid loss. That may lower blood pressure, especially when you stand up quickly. Weakness, vomiting, diarrhoea, or not eating can add to the strain. A brief faint happens when the brain receives temporarily reduced blood flow; feeling light-headed without blacking out can occur for the same reasons.

Fainting during flu is not proof of a particular underlying condition. Anaemia, an irregular heart rhythm such as atrial fibrillation, dehydration, and hypoglycaemia can each contribute and may need separate evaluation.

Lay the person flat and raise their legs if there is no injury, then loosen tight clothing and keep them warm. Do not give food or drink until they are fully awake and able to swallow. Once alert, small frequent sips of fluid and a light meal may help if they can keep them down. Do not drive, shower alone, or climb stairs until the cause has been assessed.

Record what happened: the warning symptoms, position, duration of unresponsiveness, fever, fluid intake, medicines, and any shaking or injury. This information helps a clinician distinguish a simple faint from another problem.

Call emergency services if the person does not wake promptly, has trouble breathing, chest pain, a severe headache, new weakness, confusion, a serious injury, seizure-like movements, or faints during exercise. Seek same-day medical advice for a first faint, repeated episodes, ongoing dizziness, persistent vomiting, or inability to drink.

Ask whether you need an examination, blood pressure checks lying and standing, a heart tracing, or blood tests for anaemia, glucose, and dehydration. Mention heart disease, pregnancy, diabetes, recent travel, and every medicine or supplement you take.