Hi Mary,
I have dysautonomia, and some with this problem will faint. But fainting can be from many many medical problems. It may help, if you ask your Cardio directly what can be done to stop this from happening. It's very possible, that he doesn't realize just how bad the situation is for you when these spells happen.
What kinds of testings have they done on you? Did they do the tilt table?
Hope you'll get some kind of treatments soon.
Love Lizzie