At the risk of answering as a man that has had BC but, not a cystectomy I am proposing you have simply over done the exercise. I have had a triple bypass and was told to let my body dictate how far to go (even with a schedule) and these are not "push" the envelope re-habs when they are major surgeries.
I would certainly let your surgeon know where you are at and maybe back off some on the laps for a few days. That said, walking is very good for recovery.