An update after the visit to the Vet: they did an "old dog work up" on Jimmy (who will be 9 in July - not exactly a senior citizen yet) - I had a sample of first-pee urine for them (I dipped a test strip, and saw no ketones, but pretty high sugar although I've heard human test strips aren't accurate for a dog?) and they drew blood. Eyes clear (yay!) temp normal, blahblahblah.
But a rectal probe to check his prostate showed his prostate was probably enlarged, she thought, since it had "tipped over his pelvic bones"? I did some reading on this - and Jimmy shows no signs of prostate troubles (IMO), at least not yet. (Pees and poos like a champ; and he's been neutered since he was around 7-8 months) So we're going to wait until tomorrow, to get the results of the lab work. She said maybe a 2-week course of antibiotics to rule out an infection of the prostate would be needed, if his lab work comes back looking good.
Meanwhile, the entirety of the Vet's office was fawning over what a lovable and sweet dog he is. Yep - that's Jimmy. "Mr Sweetness" - and it really sucks that all this is happening to him :-(