It's possible, Gordon. A significant behavior change can certainly signal a physical problem. At this point, a vet visit would be a very good place to start.
"We are--each of us--dying; it's how we live in the meantime that makes the difference."
"It's not what you gather, but what you scatter that tells what kind of life you have lived!"
"Be kinder than necessary, for everyone you meet is fighting some kind of battle."