That's always a tough one. As an otherwise eligible bachelor living in a singles-heavy and happenin' city, I actually feel kinda bad dating and have lately been more happy just staying single.
On the one hand, if I'm up front about my illness from the beginning, things will inevitably stall out and go nowhere. I think this is mainly because for all the girls I've dated that I'm actually interested in, they're pretty desirable in general and have plenty of other options that are not gonna potentially have their colon self destruct on them for no reason medical science can agree upon. So basically, it's an easy red flag for me to hoist up that will make them prefer to be friends or just slip out of contact with.
The alternative is to conceal my illness as long as possible, but I've never felt comfortable doing that because then I'm basically doing a bait and switch. They fall in love with a gentleman who seems healthy, active, well educated, etc, and BOOM suddenly they find out that if they follow their heart they will spend the rest of their lives being burdened by a partner who has a self destructing colon.
Oh, our honeymoon vacation to Italy? Sorry baby, gotta cancel it, I'm in here making red and brown paint in the toilet!
Better cancel our dinner plans, I'm in pain and I think I just sharted walking out to the car. Sexy, right baby?
Ah you know I can't eat any of that stuff, I have to stick to this really weird diet I've found keeps me from shitting blood everywhere
In the end, I just don't think it's fair for me to burden anyone not already in my life with dealing with something that is (and should remain, in my opinion) solely "my problem." I've had a lot of friends disagree with me when I've discussed this perspective with them: "you'll find the right one, who wants to take care of you," "if she really likes you she won't care." Yeah, I don't think that's my point -- my point is it would not be fair to them.
But anyway, silver lining to this is that when I go out on a really shitty date and they're still really into me/obsessed, the truth is a GREAT "abort" switch I can flip. I just tell them about my illness in all its gory detail and 100% of the time so far I've never heard from them again. Gotta find the positive side to every situation :)