Fainting after a bowel movement: what to know

Fainting after a bowel movement can happen when straining or standing causes a sudden drop in blood pressure. The body may briefly reduce blood flow to the brain, causing warning symptoms such as warmth, sweating, nausea, blurred vision or weakness before consciousness is lost.

Pushing hard, constipation, pain and a quick change from sitting to standing can trigger a reflex that slows the heartbeat and widens blood vessels. Dehydration, not eating, illness or medicines that lower blood pressure can make this more likely. Less commonly, fainting can relate to anaemia or an abnormal heart rhythm. A clinician may ask about the event, examine you and check blood pressure or heart rhythm.

If warning symptoms return, lie flat and raise your legs, or sit with your head lowered if lying down is not possible. Loosen tight clothing, move away from heat and have someone stay with you. Do not drive, climb or return to strenuous activity until you feel fully recovered. Once alert, sip water and take a light snack if you can swallow safely. Prevent straining by allowing time, treating constipation with professional advice and rising slowly.

Call emergency services if the person is not waking, has trouble breathing, chest pain, a severe headache, a seizure, a serious injury or new weakness or speech trouble. Seek urgent assessment for fainting during exertion, repeated episodes, palpitations, black or bloody stool, or fainting without warning. Arrange a medical review after a first episode, especially with heart disease, pregnancy, anaemia or medicines that affect blood pressure.

Could constipation, dehydration or a medicine have contributed? Should my blood pressure, blood count or heart rhythm be checked? What changes would make another episode an emergency?