Vasovagal syncope and the vagus nerve

The vagus nerve is part of the autonomic nervous system, which manages functions you do not consciously control. In a vasovagal episode, a trigger such as pain, fear, heat, prolonged standing, or straining can produce a reflex that slows the heartbeat and widens blood vessels. Blood pressure can then fall and cause reduced blood flow to the brain.

Warning symptoms may include nausea, warmth, sweating, pale skin, dizziness, muffled hearing, and tunnel vision. This explanation does not identify every cause of fainting. Dehydration, anaemia, low blood sugar, and an abnormal rhythm can resemble or contribute to the same experience.

At the first warning, stop what you are doing and sit or lie down. If safe, lie flat or on your side and raise your legs slightly. Muscle-tensing actions, such as firmly crossing your legs and tightening your leg muscles, may help while you get into a safe position. Breathe normally and wait until the symptoms have clearly settled before standing.

Avoid known settings that combine heat, immobility, hunger, or emotional strain. Keep fluids and regular meals in your routine unless your clinician has advised restrictions. Record triggers and warning symptoms so an appointment can focus on the actual pattern.

Call emergency services for fainting with chest pain, difficulty breathing, severe injury, ongoing confusion, a fast or irregular heartbeat, or collapse during exertion. Seek urgent help if there was no warning, recovery is delayed, or the person is not breathing normally.

Arrange a medical review for a first faint, repeated episodes, episodes while lying down, or symptoms that are changing. A clinician may examine you, check blood pressure and an electrocardiogram, and order blood tests when appropriate.

Ask whether your history supports a vasovagal reflex, what warning signs should prompt you to lie down, and whether tests for anaemia, dehydration, hypoglycaemia, or an irregular rhythm are appropriate.