Many people in my support forum insist they are suffering from crohn's disease and ulcerative colitis. i know it's possible, but how likely is it?

Very possible : When people are posting on specialize forums for specific diseases, they are looking for answers. So often they find comfort in knowing that there is a community of people who have the same conditions, and are who are suffering likewise. So that they can support each other, share treatment plans that has worked, share treatment plants that haven't worked, and keep informed of the latest treatments.

Possible, but off...: Many people fall victims to information abundance but lacking ability to infer anxiety & fear getting Crohn's or ulcerative colitis from the symptoms, just like many medical students imagine they may have certain diseases during their course of studying medicine. Besides, knowledge without common sense & wisdom will miss the points of adequate care. So, yes or no - probably most of times.