Infection, for one.
Another possible complication from a prostatectomy would be a bowel blockage, either physical or functional. The opioid pain meds, along with the reluctance to evacuate, could cause such a blockage, resulting in severe pain in the lower abdominal area (including hips and back) possibly with feculent vomiting and infection, of course. A genuine medical emergency - but not one that most people would like to detail publicly.