It looks like you could have a case, and obviously doctors wouldn't want you to know that. Lawyers would.
http://www.scielo.br/scielo.php?pid=S0100-879X2007001200008&script=sci_arttext
Hi......have you had your thyroid checked.....Hyperthyroidism can cause this. Also, being dehydrated so make sure you're getting plenty of water, Gatorade, orange juice and eat a banana every day to replenish your electrolytes which when low can affect your heart. If you haven't researched the side effects of the sedation they used, then do this as well. Doctors do tend to label everything as anxiety, when they need to rule out all other causes first. I assume since you have a Cardiologist that testing was done, and your heart was found to be okay. Having said this, since you feel better while on the beta-blocker then it may be anxiety. This is normally how anxiety hits us, right out of the blue and it may have just been coincidental that it happened right after your endoscopy.....or you may have had some anxiety about the endoscopy and it went full blown afterwards. But since your heart acts better on the beta-blocker I would definitely see a psychiatrist to either rule anxiety in or out, just like any other medical condition.