Overview of the Vasovagal Reflex

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Do you ever begin sweating and feeling like you are going to pass out during a bowel movement, or do you feel faint at the sight of blood? It's possible that your vagus nerve is causing this sensation and triggering your body's vasovagal response.

Straining during a bowel movement and the sight of blood are common triggers. So are stress and standing for a long time. Any of these can send you into a fainting spell called vasovagal syncope, and there are a few warning signs that lead up to it.

This article will explain your body's vasovagal reflex, what triggers it, and steps you can take to prevent or minimize these episodes.

fainting warning signs

Verywell / Jessica Olah

Overview

The vasovagal response is an automatic reflex that stimulates your vagus nerve. It can affect your central and peripheral nervous system, as well as your cardiovascular system. When triggered, the vagus nerve sends a message to the brain that may cause a sudden drop in your blood pressure and heart rate. This can make you feel faint.

The word vasovagal describes the two parts of your body that cause the response: "vaso" refers to your blood vessels and "vagal" refers to your vagus nerve.

Vasovagal Reflex Symptoms

If the vagus nerve is suddenly stimulated, several body changes may occur. These can be early warning signs of a fainting spell, which causes you to temporarily lose consciousness.

  • Dizziness or feeling faint or lightheaded
  • Suddenly feeling warm and sweaty or as if you have cold and clammy skin
  • Blurry vision or tunnel vision (blackness in the periphery of your vision)
  • Feeling nauseous
  • Ringing in your ears
  • Turning pale

Because these symptoms can sometimes be caused by another condition, tell your healthcare provider if you experience them so you can get a proper evaluation.

Causes

The vasovagal reflex is not necessarily abnormal and the nerve pathways involved are most likely present in everyone. Scientists believe this reflex developed as humans evolved and began to stand upright. The difference now is that some people are more susceptible to involuntarily triggering the reflex.

One study notes that 42% of women and 32% of men experience at least one vasovagal syncope event by the time they reach age 60. According to that study, some people tend to faint more often than others.

In some cases, there may be an underlying medical condition, such as a neurological condition (one that affects the brain or nerves), that can cause a person to experience these symptoms.

According to the National Institute of Neurological Disorders and Stroke, a fainting spell that does not have a triggering event may also be a sign of an underlying heart problem. However, it is not uncommon to find no specific cause for the episode.

Recap

Many people experience at least one vasovagal syncope episode at some point. Usually, these episodes have no specific cause, but sometimes another medical condition may be to blame. If you experience vasovagal symptoms, talk to your healthcare provider.

Treatment

If your healthcare provider identifies a specific condition that is causing your fainting spells, treatment will focus on addressing that issue. For example, medications or procedures might be needed to correct a heart rhythm problem.

If your healthcare provider does not find any medical diagnosis to explain your symptoms, you may benefit from following some basic self-care recommendations. For syncope, it's advised to do your best to avoid things that may trigger the reflex.

Possible triggers include:

  • Standing up quickly
  • Standing for too long
  • Not getting enough sleep
  • Dehydration
  • Becoming overheated
  • Emotional stress
  • Fear
  • Seeing blood

Straining during bowel movements and irritable bowel syndrome can also provoke the response.

Tips to Control Triggers

There are some things you can do when you begin experiencing the signs of syncope. Try crossing your legs and tightening your hand, arm, and leg muscles. You can also slowly lower your head toward the floor to help stabilize your blood pressure.

If stress is a trigger, keep yourself as calm as possible. Although stress episodes can be scary, you can use calming self-talk and mind-over-body practices to help get yourself through a stressful period and avoid panic. Remind yourself, too, that your symptoms will pass.

You can also find reassurance in the fact that your healthcare provider has checked you and ruled out any more serious causes of your symptoms.

Summary

The vasovagal reflex is a common cause of fainting. The vagus nerve is connected to the heart and blood vessels. If it is triggered, can lower your blood pressure and heart rate and make you feel faint. Regardless of whether you lose consciousness or not, it is important to talk to your healthcare provider about your vasovagal symptoms and what may trigger your episodes. In most cases, the response is normal, but they may recommend tests to see if there is a medical reason behind them.

A Word From Verywell

Fainting spells are common and often caused by innocent triggers, which you may be able to control. Pay attention to those early warning signs and do your best to avoid fainting. However, if you have not done so already, it is important to see your healthcare provider to rule out a serious condition.

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4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Alboni P, Alboni M. Vasovagal syncope as a manifestation of an evolutionary selected trait. Journal of Atrial Fibrillation. 2014 Aug 31;7(2):1035. doi:10.4022/jafib.1035.

  3. Raj S, Sheldon R. Management of postural tachycardia syndrome, Inappropriate sinus tachycardia and vasovagal syncope. Arrhythm Electrophysiol Rev. 2016;5(2):122-9. doi:10.15420/AER.2016.7.2

  4. National Institute of Neurological Disorders and Stroke. Syncope information page. Updated March 27, 2019.