What should you know about hyperventilation fainting?

During hyperventilation, breathing is faster or deeper than the body needs. Carbon dioxide falls, which can narrow blood vessels supplying the brain and produce light-headedness, tingling around the mouth or hands, chest tightness and a feeling of unreality. A person may faint, particularly if standing, frightened, in pain or dehydrated.

Breathing changes are not the only explanation. Anaemia, dehydration, low blood sugar and heart-rhythm problems such as Atrial Fibrillation can also cause fainting or similar symptoms. The event should be described carefully rather than assumed to be anxiety.

Help the person lie flat and raise their legs if there is no injury or breathing difficulty. Loosen tight clothing, move them away from heat and watch their breathing. Do not make an unconscious person eat or drink, and do not use a paper bag. Once fully alert, slow the breathing gently by relaxing the shoulders and breathing comfortably; avoid forceful deep breaths.

Arrange medical review after any first faint, repeated episode, injury, or episode occurring during exercise. Keep a note of posture, warning symptoms, triggers, medicines, food and fluid intake, and how quickly recovery occurred.

Call emergency services if the person is not breathing normally, does not wake promptly, has chest pain, severe breathlessness, a sustained fast or irregular heartbeat, seizure-like movements, serious injury or new weakness. Urgent assessment is also needed when fainting occurs during exertion, while lying down, or with no warning.

Ask whether you need blood tests, an electrocardiogram or heart monitoring, and whether dehydration, Anaemia, Hypoglycaemia or Atrial Fibrillation should be checked. Discuss safe breathing techniques and whether any medicine, heat exposure or fluid restriction may contribute.