Why Do Normal Bodily Functions Cause Fainting Spells?

Syncope is just another name for fainting. It's quite common for people to faint unexpectedly. I have never fainted before, until recently. I bumped my funny bone on the door casing as I was passing through it. I'm not even sure how I managed that, but the pain was so intense that I fainted. I just lost consciousness and fell down to the floor unconscious. It scared the dickens out of my family, however, by the time they got a wet cloth for my face and a pillow under my feet I had already come to.

As a nurse I have seen patients faint when they were getting their blood drawn. I just never really got why they fainted like that. I remember a patient telling me that he faints at the sight of blood. I thought he was kidding! Guess what? He wasn't kidding. Syncope can be caused by many factors. One of my friends just mentioned recently that he fainted while he was voiding. He said this was a first for him; he said he has fainted before having a bowel movement, but never while emptying his bladder.

It's quite interesting how this happens, really. When this happens we may have an inappropriate vasoresponse to our ordinary body functions, such as coughing, voiding, defecating, or just bumping your funny bone, like I did. This vasoresponse is triggered by the autonomic nervous system (ANS), and you cannot control it. The ANS is the same nervous system that gives you that fight or flight response when you get frightened.

When I bumped my funny bone, my ANS was triggered and a response was given to drop my heart rate and to drop my blood pressure, which in turn reduced the flow of blood to my brain. My body did what my brain wanted me to do, because my brain needed the blood, so it diverted the blood flow from everywhere else and made me faint. In a couple of minutes I was sitting up and back on my feet, no worse for wear.

The Mayo Clinic webpage that I was reading states, "Common triggers of vasovagal syncope include standing for long periods, dehydration, the sight of blood, coughing, urination, having a bowel movement and emotional distress. But in some cases, the cause of vasovagal syncope can't be determined."
There have been times I worked the delivery room, and expectant fathers have fainted dead away, while others were able to take an active role in the delivery. I would ask every father if they were up for it, and warn them if they fainted I could not attend to them. Usually if I would see a dad back up to the wall to "hold it up", I was already aware that he was going to faint any second, I would then encourage him a chance to leave the delivery room. More than one manly man has taken my offer and left the room until the baby came. It's quite common that the parent is so excited to have the baby coming, yet the sight of it caused the vagal response, which caused him to faint.

Before fainting you may get a sign that you are about to. When I hit my funny bone (the end of my elbow) I had severe pain and I felt dizzy, or as I call it "swimmy headed". Some of the common symptoms are suddenly turning pale in the skin, light headedness, nausea, feeling hot, sweating, yawning, feeling like you can't breathe "hyperventilation", your vision whiting out, or blacking out (many say they went blind), and not being able to hear well (feeling like you are going deaf). Then after the faint everything is back to normal. When a vasoresponse happens to an ordinary function, the ANS goes haywire. This is a life saving response to an ordinary event. Your body has over reacted.

Source: Mayo Clinic Information Page
http://www.mayoclinic.com/print/vasovagal-syncope/DS00806/DSECTION=all&METHOD=print