I went through this a year ago, and I have IBS-M. I ate really small meals the day before the interview and fasted from immediately after dinner until the interview was over. I had diarrhea all morning from the stress but chose not to take Imodium because it creates a vicious cycle of constipation and diarrhea for me. (I would have taken it 20 minutes before the interview if I really needed it, though.) All morning I prepped for the possible interview questions and practiced the 10-minute presentation I had to give. I didn't want to wear Depends, so I doubled my underwear--just in case--and had an emergency kit in my car with another pair of pants. I left home really early so I could get there with time to spare even if I had to make bathroom stops along the way. Knowing I had the worst-case scenario covered really decreased my stress. Enough that I had no problems, aced the interview (after one or two nervous blunders), and got the job. Good luck to you!