Existential sick day.
Of course, that’s not what I said when I called out. Migraine, I believe, is the term I used. So it was an affective, rather than cerebral, headache. . . .
I have had trouble with my moods in the past, and while those troubles are mostly past, I do have to pay attention. A plunge isn’t necessarily bad—everyone has bad days—but I can’t let it get out of hand.
So I took a day. I’m not much for homeopathy, but there may be something to it, mentally: allow the badness out a bit, as an inoculation against a runaway mood. I moped around in my bed for a few hours, then, having sufficiently indulged myself, got up to take advantage of the free day.
Mental homeopathy. It just might work.

I wonder if seeing your cat’s mortality made you sad. That’s not unreasonable.
You know I sympathize. Hope things are better today.