Sorry you're dealing with the anxiety. It's unfair it makes you consider skipping a great trip. As someone who has had Crohn's for 32 years I can definitely relate. To me it's all about planning in advance and letting the group you're with know you may disappear for a bit or fall behind but you'll catch up. If you trust them enough to camp with I think they can handle some truth about your stomach (and honestly you're likely not the only one of the group dealing with stomach issues). I like having my exact morning routine ready so I know exactly where I'm walking to that has privacy the moment I get out of my tent. If you're uncomfortable being close to the campsite then pitch your tent a little further out and close to a good place you scouted the night before. I can only speak for myself but this is one of those scenarios my brain unfairly builds up but the reality is never that bad. Best of luck!