I believe that there is a connection between nervousness and the digestive system. So many people feel nauseous or get diarrhea when they are under a lot of stress.
I don't know how it works exactly, but I do know that it happens. I had diarrhea for a whole month after starting my stressful new job, and I had nausea for months.
I didn't have any other symptoms, so I knew that it was due to my nervousness. I'd heard of having a nervous stomach before, but that was the first time I had experienced it firsthand.