Hi...more info would be needed to see if we can offer some insight.
DO u know does he suffer from Headaches....or other issues.Does he move his bowel on a regular basis....does he have IBS?...or acid reflux?
I would suggest he see a GI dr this is not normal.
"selma"
Sounds like he may have a supersensitive vagal response to defecating. Has he seen a gastrointestinal specialist about this? That must be awful! Some people I believe can have vomitting accompany irritable bowel syndrome. I really think if he's never been evaluated and diagnosed, he should get a referral to a GI specialist!