Congratulations!!! I, too, had CIS and went through the BCG treatments, mainenance treatments, and then...now I have been "all clear" for a total of 4 years!!
BCG is, as you noted, usually just "uncomfortable" but some patients have real problems with it. Twice, in my case, we had to delay treatments due to BCG-induced cystitis. Mike, whom you have probably met on these pages, had a horrible time and "failed" when the BCG had to be discontinued. In very rare cases, the side effects can be life-threatening.
That noted, it is, indeed, a life saver for many of us. Studies have shown that when problems arise the dose can be lowered significantly. At the end I was on 1/3 of the initial dose; doses down to 1/10th have been effectinve. In fact, my urologist explained that there is no scientific reason for the dose being used....that was just the way the material was packaged and available when it began to be used for bladder cancer treatment!
Good luck for your continued health. Will you be undergoing maintenance therapy with BCG?
Sara Anne