I have an autonomic disorder (along with MS) which causes me to get dizzy & pass out too.

In case nobody told you- they don't stand you bolt upright really fast during a TTT, it really was a rather boring slow movement. I thought- "this is useless, its not going to show squat, just a waste of money" Then bam- symptoms hit and I puked, sweated wildy and passed out which was new to me. Woke to nurse telling me they were able to confirm diagnosis and MD would explain course of treatment in a few moments.