Causes of a vasovagal reaction include pain, situational stressors, and straining with urination, coughing or bowel movement, states MedicineNet. Other triggers include fear of bodily injury, heat exposure, the sight of blood and standing for a long time, notes Mayo Clinic.
A vasovagal reaction is a primary cause of fainting and occurs from the disruption of acetylcholine and adrenaline, reports MedicineNet. Adrenaline is a chemical that narrows blood vessels and increases heart rate, raising blood pressure. Vagus nerve stimulation can lead to excessive production of acetylcholine, causing dilation of the blood vessels and reduction of the heart rate. This action interferes with the movement of blood to the brain, causing a vasovagal reaction.
Some people faint due to situational stressors such as receiving bad news, experiencing the sight of blood, or observing an operation or autopsy, says MedicineNet. Other people experience postural hypotension, which is a condition in which the body does not effectively regulate blood pressure, especially when standing up too quickly from a lying position, explains WebMD. This causes fainting and is common in older people, especially those with poor muscle tone.
Although a vasovagal reaction is no not typically harmful and does not require treatment, a person can injure himself during this episode, states Mayo Clinic. Patients may require tests to prevent severe causes of vasovagal reactions.