Increased anxiety about cat? (18)

Some of you may be familiar with my cat Charles, who I’ve posted here several times. He’s almost 19, and doing pretty well all things considered- he still eats and loves treats, plays a bit, and has healthy opinions about things I do.

But recently I’ve been feeing this kind of overwhelming anxiety about him. There’s no real reason- checkups go well and his behaviors are normal, ie scoring well on “quality of life” tests- but I’ve been anxious that I’m missing something and I’ll come home from work to find him sick or passed on and then I’ll feel guilty about not being there.

I cannot emphasize enough that he is legitimately, professionally-assessed-as FINE, but my stupid brain cannot comprehend that and keeps worrying. Anytime his behavior for the day shifts slightly, or even if I just haven’t been home in a while, I get paralyzingly anxious and can’t think about anything else. Has anyone else experienced this? Do you have any tips or tricks?