Prior to flying, I printed off a 3-4 sentence explanation of IC and cut them into ten slips. I highlighted the section that explains that people with IC can sometimes feel the need to urinate 50-60 times a day. I booked all of my seats at the back of the plane as close to the restroom as possible (and picked aisle seats). I learned after my flights that when you book your plane tickets you can mark a section under "disability" so that there is a record in the computer that you have a medical disability. Some online airlines have blank fields where you can fill in the disease.
Immediately upon entering the plane, I would smile at the first flight attendant that I saw and I would hand out one or two of the strips and ask if they could read it while they were getting ready for take-off. The response to this was varied: some flight attendants gave me extra special attention during the flight (and alerted both the pilot and the other flight attendants of my condition); personally thanking me for the print out and hoping that my flight was ok; asking what my paperwork "implied" and then crumpling the paperwork and handing it back to me; to flight attendants offering ice chips instead of a drink so I stayed hydrated. In general I had more positive and supportive flight attendants than negative ones, but I did have a confidence about the flight (and the possibility of being delayed on the runway) knowing that I had proactively alerted the crew to my potential special needs. One flight attendant even walked out with me into the airport and said that with the new FAA regulations that I had done a good thing by alerting them ahead of time because it could be an issue to use the restroom when the seatbelt sign was lit. Another flight attendant stated that because it was a medical condition that had to comply but I needed to know that if I walked around the plane when the seatbelt sign was on that the airplane could not be held liable if I fell during turbulence, etc.
Overall I am thrilled to report that I am one step further to being a "normal" person. I will always be an advocate for those of us walking around (and traveling) with hidden diseases. May your travel be as good as mine.