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Vasovagal Syncope

The most common type of syncope is called vasovagal syncope. A variety of situations stimulate the vagus nerve, which leads to a slowing of the heart rate and dilation of the body's blood vessels. With a slow heart rate and dilated blood vessels, less blood gets to the brain, and fainting occurs. Pain and emotional stress can trigger vasovagal syncope in susceptible people. This type of syncope can happen more often in some families.

From Wikipedia

Triggers

Typical triggers for vasovagal episodes include:^[1]

• prolonged standing or upright sitting, particularly when standing with legs in a locked position for long periods of time. Avoidance of long-term locking of one's legs in the standing position is taught in the military, as well as marching band and drill team.
• stress
• any painful or unpleasant stimuli, such as
  • giving a blood donation or watching someone give one
  • watching someone experience pain
  • watching/experiencing medical procedures
  • sight of blood
  • occasions of slight discomfort, such as dental and eye examinations
• hyperthermia, a prolonged exposure to heat
• sudden onset of extreme emotions
• hunger
• nausea or vomiting
• dehydration
• urination ('micturition syncope') or defecation ('defecation syncope')
• abdominal straining or 'bearing down' (as in defecation)
• swallowing ('swallowing syncope') or coughing ('cough syncope')
• random onsets due to nerve malfunctions
• pressing upon certain places on the throat, sinuses, and eyes
• high altitude
• use of certain drugs that affect blood pressure, such as amphetamine
• intense laughter^[2]

The cornerstone of treatment is avoidance of triggers known to cause syncope in that person. Before known triggering events, the patient may increase consumption of salt and fluids to increase blood volume. Sports and energy drinks may be particularly helpful.

Yeah, good times.