Well, to my horror, it has still not stopped. It does stop sometimes, for as long as a few hours, but it always comes back.
I have now tried magnesium tablets. It did stop for a while after I took one, but then it came back a few hours later, so that might just be coincidence. I'm definitely not short on potassium or magnesium, though. And although I do my best to avoid salty stuff, there's no risk of me not getting enough salt. I have enough salty foods that I'm more likely on the "too much salt" side of things (as most modern western folks are).
I would say stress, but strangely, I'm not that stressed. I got my visa and have already completed all the relevant paperwork and bureaucratic nonsense. I have four days off a week including weekends, until the school year starts. My boss is a fucking douchebag and I want to rip his balls off, but that's been that way for a long time, and I only have to work three days a week anyway (and half the time he's not even there). If anything, I'm under far LESS stress right now than I have been in ages.
I would also say exhaustion, but all I've done for most of today is sleep. Yesterday was definitely exhausting, but this has been going on for like four or five days now, and I take naps and rest all the time.
I'm even cutting back on caffeine, just in case that's the culprit. I don't normally have more than two or three cups of coffee/tea per day, but yesterday I had none and today I had only one (and that only because I had a splitting headache from caffeine withdrawal - even two cups a day is enough for me to be hooked).
So I'm really stumped, here. I've hardly gotten any exercise since this started. Originally I assumed it was the result of all the extra exercise I was getting, but shouldn't my muscles have chilled out by now? It's really quite irritating.