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? It's possible that your vagus nerve is causing this sensation and triggering your body's vasovagal response.

Common triggers include straining during a bowel movement or, for some people, the sight of blood. Either of these can be enough to send you into a fainting spell called vasovagal syncope and there are a few warning signs that lead up to it.

fainting warning signs
Verywell/Jessica Olah


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.

The word vasovagal describes the two parts of your body that cause your body's 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 that cause you to temporarily lose consciousness.

  • Dizziness or feeling faint or light-headed
  • 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
  • A ringing in your ears
  • Turning pale

Because vasovagal symptoms can sometimes be attributed to another condition, bring any symptoms to the attention of your doctor for proper evaluation.


The vasovagal reflex is not necessarily abnormal and the neural 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 percent of women and 32 percent of men will have experienced at least one vasovagal syncope event by the time they reach 60. It also agrees that some people tend to faint more often than others.

In some cases, there may be an underlying medical condition, such as a neurological condition, 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 that no specific cause can be found.


If your doctor 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 adequate sleep, dehydration, and emotional stress. Straining during bowel movements and irritable bowel syndrome can also provoke the response. If you're sensitive to the sight of blood or having your blood drawn, you may also experience syncope.

Tips to Control Triggers

There are some things you can do in the future when you begin experiencing the signs of syncope. Try crossing your legs and tightening your finger, 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 such episodes can be scary, you can use calming self-talk and mind-over-body practice to help get yourself through a stressful period and reduce panic. Remind yourself that your symptoms will pass as well.

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

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 counteract it. However, if you have not done so already, it is important to see your doctor to rule out a serious condition.

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Article Sources
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  1. Da silva RM. Syncope: epidemiology, etiology, and prognosis. Front Physiol. 2014;5:471. doi:10.3389/fphys.2014.00471

  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.

Additional Reading
  • National Institute of Neurological Disorders and Stroke. Syncope Information Page. 2017.