After I decided that I might not, in fact, be dying, I decided to get up to see if I felt better, or, at least, less bad when standing. It was hard to tell. Sitting on the bench in front of the toilet did feel somewhat less bad, though, so I did that for an hour and a half, with occassional position changes to see if the cramps were an indicator of some alien wanting to come out one way or the other. Apparently, not.
Around 4:30, I felt not-bad enough to get back into bed, and I fell asleep pretty quickly, fortunately. I've had recurring cramps of varying intensities since then, and when I'm not cramping, I feel generally tender, and the mere thought of food is unappealing.