I've only had a rectal one, which started as a really painful abcsess. So yes, I knew for sure that it was there. I'm guessing it might be harder to know when they are up inside at first. I can imagine there would also be pain, possibly fever from infection at some point. I've also heard of passing fecal matter, gas, and blood in the urine with those as well.
Diagnosed with Crohn's Disease 2/06 after sever GI bleed. Has been suffering since 1998. History of rectal fistula and gallbladder removal. Taking Asacol, Questran, Toprol XL (for high blood pressure). Tapered off prednisone a month ago!