When you worry about things you get diarrhea why?

When you worry, the body is under stress. The body releases fight or flight hormones to help deal with the stress. These chemicals are mainly adrenalin and noradrenaline. Cortisol is also elevated. These chemicals act a bit as stimulants too. The stimulants may have effects on the intestines. When you are emotionally distraught, your digestion is poor, and the body expels what it cannot digest.

Some may hypothesize that the body has evolved to deal with war and civil unrest. So diarrhea and constipation would be part of the preparations. You can't stop to defecate during a heated battle, so the body would eliminate before the battle as things get stressful.