FinLady, does it feel like a lactic-acid build up feeling?
I have no dx, but I get this feeling sometimes when my sx's flair up, and I'm walking around too much (at the mall). It's combined with a stiff thigh feeling kind of....

Once I woke up in the night thinking there'd been an earth tremor!! I asked friends the next day, and there hadn't been one... I must have been tremoring.. very weird, as I was asleep.