Why do I have to have a bowel movement when I get nervous or when I can't get to a bathroom?

Mammal stress call. Many species "relieve" themselves as an initial stress reaction. It makes it easier to flee or to fight without the burden of a full intestine. Psychotherapy may help you learn how to avoid some stress and how to be prepared for it when it has to be dealt with. Your pcp may also have suggestions for diet and medication options. Best.