Two experiences...
First was a chemical (I guess Nuclear) but can't remember. Lying in a big thumping (open) tube, with needle in the arm for injecting the "whatever"... I could look back and see a big TV screen that showed the valves in my heart, opening and closing... fine... very interesting... until... whoompf!!! it felt like King Kong had picked me up and was crushing my chest... the world went black, and I came to... thinking "did anyone get the licens plate number of that truck?" Anyway, all ok... passed w/flying colors.
Second was three years ago, not sure why... It was the treadmill test. As others explained... Doctor, nurse, two attendants, and me, wearing this heavy harness. Was doing fine, as treadmill accellerated, but for some reason, my pusle rate wouldn't go up, so the incline ramp raised... still couldn't get the blood pressure or pulse up to where the doctor wanted... It was a long time, and I was getting tired, but "keep on going"... started sweating, and the room began to get fuzzy... still not where the doctor wanted the readings... sheesh... Finally the two big guys who were holding me up decided I'd had enough, and I was led... to a seat where they contuinued to read the harness, electronically... Doctor was leaving the room... and nurse SCREAMED
"DOCTOR!!!!". My heart had apparantly stopped. Panic set in, and everyone rushed around, doing what I don't know... Nobody said "code blue", so that made me feel better.
Anyway, I was awake the whole time, and actually feeling quite good. The doctor was busy reading the paper tape print out, and the staff still looked panicky. After a minute or two more, the doctor looked at me, and said "you're fine... nothing wrong... "It was just an ANOMOLY" And so I learned to love that word.