I called my regular dentist, and she said rest, massage, moist heat, and no talking or chewing, if it's not better in a week, come in and she'll look at it (self-employment has lousy insurance benefits, so I'd rather do what I can at home before I pay $$ for a doctor). She said that what happens sometimes is that one of the discs that sits in the jaw socket gets shifted or pushed out of alignment, and that it will very often reseat itself, but it takes a while for the pain to go away. She said the mouth guard might help, especially when I'm doing heavy lifting, so I'll try that.
I''m for sure positive that I don't grind my teeth, though...I am in either a dentist's or periodontist's office 4-6 times a year, and there is no evidence that there's ever been any undue pressure or abrasion on my teeth. I'm pretty sure that I slept on it funny, then exacerated it by driving several hours and helping some friends move. We'll see if I can make it go away on its own, but if it continues another week or so, I'll be going into the dentist for a look-see.