Why do I get intense chills and goose bumps when I have to have a bowel movement or urinate?

Goose Bumps . Sometimes when one strains at the stool or urinates, the intra abdominal pressure rises (this is called a valsalva) and the increased pressure sets of a chain of reactions that affects your para sympathetic nervous system and your get goose bumps, chills, and often a lightheaded feeling. Try not to strain so much with either activity and let things naturally empty.