It's finally tapering off, and in doing so, it's feeling more and more like regular reflux. I have a lot of symptoms of that on a regular basis, although an endoscopy last year was negative, so I'm not being treated for it at the moment, and assumed that meant I didn't have it. However, in googling a bit, I have found that Endoscopy-negative reflux disease is totally a thing (thanks, NIH!). Going to try some more of the omeprazole that I still have and see if that settles things down in a week or so. If so, I'll be talking to my doc more about it in March.

I was most nervous that it might be cardiovascular, and the less and less that looked likely, the happier I was. I tend to guess "weird neurological thing" more often than most, just because so many of my fibro weirdnesses have been that sort of thing.