When should you worry about fainting if you have low blood pressure?

A drop in blood pressure can briefly reduce blood flow to the brain, leading to light-headedness, blurred vision, collapse or a short loss of awareness. Dehydration, illness, heat, prolonged standing and some medicines can contribute. Fainting may have other causes too, so a new episode deserves a clinical review, especially if the circumstances are unclear.

Lie flat and raise your legs if possible, loosen tight clothing and stay still until you feel fully recovered. Do not drive, climb or bathe alone until you have discussed the episode with a clinician. Write down what you were doing, warning sensations, injuries, medicines, food and fluids, and how quickly you recovered. Stand slowly and keep hydrated unless a clinician has restricted your fluids.

Call emergency services for fainting with chest pain, severe breathlessness, a racing or irregular heartbeat, seizure-like movements, serious injury, confusion, weakness on one side, trouble speaking, heavy bleeding or failure to wake normally. Seek prompt medical assessment for a first episode, repeated fainting, fainting during exercise, or collapse without warning. A clinician may check blood pressure lying and standing, review medicines and arrange heart or blood tests.

Could my medicines, dehydration or another illness be lowering my blood pressure? Should my blood pressure be checked in different positions? Do I need an electrocardiogram or further tests? Which activities should I avoid until the cause is clearer?