Relle, there was a thread in here a couple of weeks back about the exact same thing, I can't remember who posted it, but there were quite a few qomen who experience it. Including me - you are right, I would describe it as feeling exactly like the baby is having a fit, is a real spasmodic repetetive jittering sort of feeling. Freaked me out the first time I felt it, and was so strong it took my breath away!

You are also right about it being ace having Alan around!