Rachel,
I'm not sure if this might help but my mom who has celiac disease also had trouble with heart racing and this feeling of about to pass out. They ran all kinds of tests. Her blood pressure was low and then high. She had been on meds for high blood pressure for years prior to this. They finally figured out it was Addison's disease after 3 hospital and 3 emergency room visits. She would get better, be released to go home and then have another episode at a later date.

Also, I had trouble with heart racing when I began to drink green tea. I do not drink it now. I have heard that it is stronger in caffeine but I'm not sure of this. I do know that cutting out caffeine is not immediate. My doctor told me that the liver holds it for up to thirty days so you can have problems with it for a long time after stopping it. You may already know all this but it just popped in mind that maybe it could help you.

Beth