Diarrhea and fainting: what should you know?

Repeated loose stools remove water and electrolytes. This can reduce the blood circulating through your body, especially if you are also vomiting, sweating, or unable to drink. A sudden drop in blood pressure may cause dizziness, blurred vision, weakness, or a brief loss of consciousness. Fainting can also have other causes, including low blood sugar, anaemia, an irregular heartbeat such as atrial fibrillation, or a separate heart problem. Diarrhea itself does not identify the cause.

If you feel faint, lie flat and raise your legs, or sit with your head lowered if lying down is unsafe. Do not drive or climb. Once fully alert, take frequent small sips of water or an oral rehydration drink; a pharmacist can advise which product suits you. Stand slowly and have someone stay nearby. Note how often you pass stool, whether there is blood, what you have managed to drink, and what happened before the faint.

Call emergency services if the person does not quickly regain awareness, has trouble breathing, chest pain, a seizure, a serious injury, confusion, or a new irregular heartbeat. Seek same-day medical care after any faint with ongoing diarrhea, very little urine, severe weakness, persistent dizziness, blood or black stool, or severe abdominal pain. Children, older adults, pregnant people, and anyone with heart or kidney disease can become unwell from fluid loss sooner.

Ask what may have triggered the faint, whether your blood pressure and heart rhythm need checking, and whether blood tests are appropriate. Discuss a safe rehydration plan and which medicines should be paused or reviewed while diarrhea continues.