Ha! I feel like an idiot now, I didn't realize cystitis was a uti! Whoops! That definitely isn't what my friend had then.
MnG, so you have had that lovely test for it too then! When I went in I told them there was NO.WAY that I could drink as much as they were asking me to, as far in advance as they were asking me to, and hold it that long. I actually kind of laughed at them. They told me start drinking it when I thought I needed to in order to make it REALLY full and really have to go when I went back. I cut the time in half; well of course that was the one time in my whole life that my bladder wanted to behave like it was supposed to, and when I went back I only barely had to go! She checked and said the water hadn't made it from my stomach to my bladder yet so we had to sit there and wait.

At least I was scheduled for another test that they could do while we were waiting! Then I got to experience the wonderfulness that you're referring to of them pressing down on an uncomfortably full bladder. :/