So by my calculation you'd be roughly 45 or 46 now so I'm guessing it is not old age creeping in.
Since urologists do things like BCG treatments for people who may have severe reactions and need to get in touch with the doctor, there is typically a urologist on call or way to call in and get a message to the doctor. If yours isn't the one on call the one who is can usually get in touch with yours to find out what the ASAP was about or have your doctor call you.
Had they not put that "ASAP" in the message, then it may have been tricky reaching someone on their day off but if you called their answering service and said "He left a message saying to call ASAP, please have him call me ASAP because now I'm freaking out (even if you weren't) then it is likely they would have gotten a message to him.
It is Monday now anyway but I'd have suggested that for Friday and over the weekend.
There has to be a way to get in touch with doctors in an emergency situation. If they hadn't used that darn "ASAP" acronym, it probably wouldn't have been a big deal for you. Using it in the message like would put anybody into a state of concern until they can get back in touch.
I hope it is not bad news. Let us know when you find out today.
Mike