Hi Sean, sorry about your diagnosis. Welcome to the medhelp group though! you can find lots of support and wonderful help on here!!
I have similar issues with feeling like I cannot feel my heartbeat... my bp gets very low and that seems to be when I have my intense issues. I wear support stockings(http://www.amazon.com/Relief-15-20-Closed-Support-Silicone/dp/B0012XRFKW/ref=sr_1_15?ie=UTF8&qid=1391789338&sr=8-15&keywords=15-20mmhg+compression+socks ) to keep my bp up. I have been wearing them for 4 years now. they help immensely! I also drink a lot of water, and a Gatorade every morning. When I was diagnosed 5 years ago a day of walking 10,000 steps would put me in bed for three days and I would have awful symptoms. I have been working on increasing my steps and now I am up to 15,000 :) with no symptoms. I cant completely get rid of the compression stockings yet but I can go without them for a day at a time... There are cheaper places to buy them too... I used a total gym to start exercising as much as possible without having to stand, because I couldn't at first. I also cut out gluten in my diet for the past year and a half and that seems to help tremendously. My fitness level is nowhere near what it was when I was younger but I am getting healthier and more active one day at a time... let me know if you want to find anything specific!
I cannot give you an answer on what causes it, but I have POTS, dysautonomia and Chiari.
First, if you are feeling crummy and getting worries about your health, it wouldn't be far fetched you will have some sort of anxiety, but I do not necessarily think that the anxiety is a trigger. (Which came first-chicken or egg). Probably weird/scary symptoms then anxiety. But that won't solve the problem.
Secondly, it is very common for the 24 halter, echo, stress tests to come back normal because that is not where the problem lies. I had a loop recorder heart monitor implanted. It was the size of a small jump drive. And my episodes were in the am and in a hot environment like a shower, and straining like climbing stairs or lifting my arms above my head.
Try this: get a wrist blood pressure monitor and take it laying down. Then stand up and take it again. Record all your results. (Have someone with you in case you pass out). These are the things your doctor should be doing in his office so he can see the difference in readings. Also try taking it during times you feel bad and what you were doing to identify triggers.
You need a cardiologist that is versed in POTS. Florinef worked well for to to raise my blood pressure.
If you need tips to help you feel better, let me know. I don't know how much information you are searching for.
Best of luck!