What Causes Rolling Muscle Spasms In Stomach?

i noticed a rolling spasm in my stomach a few weeks ago. Not a period cramp or a bm cramp. def a muscle thing. I grasped my stomach when it happened, ( low left by bellybutton) and i felt a knot. as I kept grasping and kneading, i felt it roll and disappear. I have probed the crap out of my stomach since to make sure there are no masses of any kind. Cant feel anything. last night had another one after I almost had a collision with a drunk driver and I had to swerve really hard to avoid the accident. I have IBS, diabetes and am peri menopausal, taking 500mg x4 tid metformin lipitor x1 tid and 20,000 mg Vitamin d once a week. Any ideas?