UPDATE -- We just got back from the vet, and she said that based on the physical exam, everything looks and feels good, so there's nothing urgent that we need to be concerned about. (Which, I suppose, means that for now at least, I can stop hovering over him and watching him breathe and obsessing over every swish of his tail.)
She said that as the metronidazole seems to have a positive effect on General's stools, this is an indication that there was defeinitely some sort of bacterial imbalance going on in General's gut.
We're doing bloodwork and a urinalysis just to check for anything else going on and to compare to the bloodwork he had done last year in which everything was a-ok, with the exception of a slightly elevated amylase level. This, she said, would again point to issues in the gut, but to note that the level was only slightly evelvated, and that we would see how that compares to the new results tomorrow.
In addition to the slight behaviour change/irritability, I mentioned to her that I noticed him swallowing a bit more than usual, and he did it a few times while we were there. She mentioned that with cats, even if they may not be vomiting, the swallowing can be a sign that they are feeling nauseous. While this can be caused by any number of things, one thing that does occur in senior cats is ulcers. She said that the symptoms of ulcers in cats can be treated using over the counter Pecid AC, and that if we do that and find the suspected nausea and symptomatic excessive swallowing stops, then we can look at the best way to fight the bacteria that has been shown to cause ulcers in the first place. Unfortunately for poor General Bear, that may include a combination of metronidizole (sigh...) and... I think she said amoxicillin. But we'll see how things go.
So, that said, everything, at least in the immediate future, looks good for General's health. Yay!
I'll get the results of the bloodwork and urinalysis tomorrow.