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Why does it happen? What are the triggers? And how can I prevent them?

Vasovagal syncope is the medical term for a simple faint.

This type of faint occurs due to an exaggerated response by the automatic (autonomic) nervous system.

This response leads to a drop in blood pressure and often a slowed heart rate. When blood pressure drops, less blood flows to the brain, leading to fainting.

Once you've fainted and are lying down, more blood flows to the brain — because it's no longer pumped upward against gravity — and you regain consciousness.

Triggers for a common faint include:

  • Standing for prolonged periods

  • Dehydration

  • Coughing

  • Urination

  • Having a bowel movement

In some cases, the cause can't be determined. After a vasovagal faint, you typically regain consciousness quickly. But you may feel washed out or tired for a few minutes or hours.

Adults who faint often have a history of fainting as children. A vasovagal episode may cause a near faint (pre-syncope) or total loss of consciousness (syncope). But in either situation, you regain consciousness on your own.


Before a faint, you may have warning signs and symptoms, such as:

  • Pale appearance to skin

  • Feeling of warmth

  • Weakness

  • Lightheadedness

  • Nausea

  • Yawning

  • Sweating

  • Rapid breathing (hyperventilation)

  • Blurred vision

  • Difficulty hearing

If you have any of these signs and symptoms, lie down promptly. This may help avoid a faint.

If someone else faints, don't try to hold them upright in a chair. This may prolong the spell by impeding the return of blood to the brain.

If after fainting, you have slurred speech or difficulty moving an arm or leg, get immediate medical help. These signs may indicate a stroke.


If you're prone to fainting, these tips may help:

  • Avoid triggers for fainting, if you can identify specific ones.

  • Drink plenty of water and don't skip meals. Dehydration and not eating can lower blood pressure and intensify blood pressure changes due to changes in position.

  • Rise slowly from a lying or sitting position to allow your body time to adjust.

  • If you feel faint, stand with your legs crossed and thighs squeezed tightly together (scissors position).

  • Vasovagal fainting is common and usually not serious. It's important to distinguish the common faint from more serious causes of loss of consciousness, such as heart rhythm disturbance (arrhythmia) or epilepsy. A 2003 study found that people with multiple potential causes of fainting have an increased risk of an earlier death than do those with only a single potential cause. If you have unexplained faints, see a doctor for a complete evaluation.


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