(likely) post-car collision (apparently this is a thing, but I don't think my situation was that intense, so it's hard to believe my body would think it experienced some kind of physical trauma, but who knows. I mean, it was kind of intense, but it wasn't like a serious car accident that totals the vehicles. The more I think on it, the more likely this seems the culprit though. Not sure if that means I should go to the Doctor's).
(less likely, but possible) Peri-menapause :(
(least likely) pregnancy. It's just very unlikely because we're very careful.