It connects the digestive system to the brain, and it's job is to manage blood flow to the gut. Vomiting, bearing down to have a bowel movement, or conditions that drop blood pressure amplify the effects of the vagus nerve and redirects much blood to the gut which may lead to fainting.
http://healthquestions.medhelp.org/fainting-during-bowel-movement
Combining those effects drains the brain and turns out the lights. Like shock, losing consciousness due to alcohol is not technically considered fainting, but it may or may not be cause for concern. It is possible to die from alcohol poisoning, and passing out is a sign of serious intoxication.
https://www.verywell.com/causes-of-fainting-1298399
1 doctor agreed: Dizziness: Hello, after a bowel movement, the body squeezes which causes a temporary shift in blood flow away from the brain. This is referred to as a valsalva maneuver. The dizziness should be short lived. If it persists, follow up with your doctor. Blood pressure checks, labs, and a careful examination may be needed.
https://www.healthtap.com/topics/dizziness-during-bowel-movement
Feeling like I was going to pass out from nausea and dizziness, I had a small bowel movement (diarrhea) followed by the best passing of gas in my 34 years. Recovery seemed to get a lot easier from there. I've been home now for 8 days.
http://healthquestions.medhelp.org/fainting-during-bowel-movement
I start to feel faint, never faint all the way. Then upset stomach and one loose bowel movement. And I get really hot. after I use the bathroom it all goes away. Sometimes it hits me in the middle of the night and wakes me up then usually lasts most of the next day. I am 59 and weigh 140 # and this has been going on off and on for 3 years.
http://www.healthcaremagic.com/premiumquestions/Fainting-with-upset-stomach-and-loose-bowel-movement-Anxiety/66748
Dizziness, Excessive sweating, Fainting and Frequent urge to have bowel movement. WebMD Symptom Checker helps you find the most common medical conditions indicated by the symptoms dizziness, excessive sweating, fainting and frequent urge to have bowel movement including Fainting (vasovagal syncope), Middle ear infection, and Labyrinthitis.
http://symptomchecker.webmd.com/multiple-symptoms?symptoms=dizziness%7Cexcessive-sweating%7Cfainting%7Cfrequent-urge-to-have-bowel-movement&symptomids=81%7C228%7C261%7C109&locations=2%7C66%7C2%7C20
November 7, 2011 was the first time this happened to me - intense, pounding headache during bowel movement. During the middle of the bm the pain crept up the left side of the back of my neck and with every heartbeat pulsed into my head, primarily on the left side.
http://healthquestions.medhelp.org/fainting-during-bowel-movement
Vasovagal reflex: Dizziness, and even fainting, with moving the bowels is due to a reflex of the involuntary(autonomic) nervous system called the Vasovagal reflex. This reflex causes the heart rate to slow and the blood vessels in the legs to dilate, both causing a lowering of the blood pressure.
https://www.healthtap.com/topics/dizziness-during-bowel-movement
There are 56 conditions associated with dizziness, excessive sweating, fainting and frequent urge to have bowel movement. The links below will provide you with more detailed information on these medical conditions from the WebMD Symptom Checker and help provide a better understanding of causes and treatment of these related conditions.
http://symptomchecker.webmd.com/multiple-symptoms?symptoms=dizziness%7Cexcessive-sweating%7Cfainting%7Cfrequent-urge-to-have-bowel-movement&symptomids=81%7C228%7C261%7C109&locations=2%7C66%7C2%7C20
Fainting (syncope) is a sudden loss of consciousness from a lack of blood flow to the brain. People who faint usually wake up quickly after collapsing. Management for this condition is simple, usually requiring little more than letting the victim recover while lying flat (supine).
https://www.verywell.com/causes-of-fainting-1298399
what causes fainting when doing a bowel movement
The vasovagal reflex causes fainting when doing a bowel movement. Vasovagal reflex causes fainting when doing a bowel movement. 