In a nutshell
Pain, fear, or prolonged standing can trigger a circulatory reflex with nausea, sweating, and lightheadedness in some people. If blood flow to the brain falls far enough, a brief faint can occur.
Why does it happen?
Autonomic circulatory control changes vascular tone and sometimes heart rate. Blood vessels dilate and/or the heart beats more slowly. Blood pressure falls, so temporarily less blood reaches the brain.
Frequency
Vasovagal circulatory reactions occur in the population, but individual susceptibility differs greatly. Near-fainting, a single faint, and recurrent syncope should be counted separately.
Frequency is a qualitative description, not your individual probability.
Is it normal?
Lie down immediately at warning signs to avoid a fall; new fainting should be medically assessed.
When to seek advice
Fainting during exertion, with chest pain, shortness of breath, injury, or failure to recover quickly: call emergency services. Do not provoke it by holding your breath or straining.
Does this happen to you?
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Sources (1)
- Vasovagale Episode – StatPearls (opens a new tab)
The overview describes triggers, blood-pressure drop, and possible slowing of heart rate in reflex syncope.
Editorial update: . AI-assisted research and editing; not individually reviewed by a physician. How we research
