And so we went to the vet. After a quick once-over, the vet declared that Rey is not in any imminent danger -- YEA! -- but agrees that something may be bedeviling him. So blood was drawn. It should reveal whether the problem is his kidneys, his thyroid, or something else.
If the vet were a betting man, he'd put his money on hypothyroidism. While serious, with potential impact on all Rey's organs, it's also easiest to treat.
Fingers crossed that we can find a way to keep my little man happy, engaged and comfortable for as long as we can.