Just thought I should update, in case anyone else comes across this situation.

This morning I woke up with NO pain at all in my lower body. Abs still screaming at me, but actually my legs and butt feel better than they did before the workout. Tired, but not sore. Very surprising.

It is probably largely due to the amount of deep stretching and massage I did on my lower body last night. Usually, I'm not a very diligent stretcher, but last night I was particularly worried about how my legs would take the workout, so I even ran a hot bath and did some stretching in there, too.

It also indicates to me that I was probably right that there was no actual damage from the Pilates workout, just general soreness. Otherwise, I think it would hurt just to walk today, and it doesn't.