• Question: why do people pass out?

    Asked by maciej to Alison, Artem, Caroline, John, Gunther on 19 Jun 2012.
    • Photo: Artem Evdokimov

      Artem Evdokimov answered on 19 Jun 2012:

      Depends on specifics: could be exhaustion, pain, lack of food or water, injury, lack of sleep, low blood pressure, excitement, lack of air, too much air (hyperventilation), high g-forces, and so on – the list goes on. I suspect you’re also asking what is the actual mechanism for passing out (Syncope in medical terms) – most of the time it is caused by transient drop in blood supply to the brain. Please note that a significant drop in blood supply can cause death or brain trauma! Fainting can be a benign condition or it could be a sign of a very serious health problem (cardiac issues for example).

      Syncope can be either caused by circulatory problems (typically with one’s heart) or by a reflex, another common form is caused by transient blood pressure drop due to change in posture (getting out of bed, in some cases!).

      Most of us will experience fainting at least a few times in our lives, most commonly either before age 10 or after age 50-60.

    • Photo: John Short

      John Short answered on 19 Jun 2012:

      Usually when I’ve had too much to drink! Alcohol is a depressant, and as a drug it will cause drowsiness and eventually you to pass out.

      Low blood sugar is also a common thing, where people who do lots of exercise, marathon running for example or footballers, or even do lots of work e.g. in an office and do not keep hydrated and do not eat will pass out.

      Bad circulation can be a factor, such as soldiers who are forced to stand for long periods of time without moving can faint.

      Shock, be it physical or mental is a huge common factor. Emotions like fright, pain, anxiety, or shock can affect the body’s nervous system, causing blood pressure to drop. This is the reason why people faint when something frightens or horrifies them, like the sight of blood. When someone faints, it’s usually because changes in the nervous system and circulatory system cause a temporary drop in the amount of blood reaching the brain and is increased to your other vital organs. When the blood supply to the brain is decreased, a person loses consciousness and falls over. After lying down, a person’s head is at the same level as the heart, which helps restore blood flow to the brain. So the person usually recovers after a minute or two.

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