Severe rectal pain during bowel movement causing fainting. what condition is this?

Defecation syncope,: Is what you are describing. Significant vagal nerve stimulus from painful defecation or heavy bearing down. This is due to the Insulin resistance syndrome, get checked for this and follow a low-glycemic index diet and get frequent, aerobic exercise. But why so much pain with defecation? You need to see a gastroenterologist to figure this part of it out.