I just found out 2 months ago that I too had anxiety after 2 trips to the ER , 1 for chest pain (was unfamiliar with the pain was the first time I had it) and the other for difficulty breathing (once again didn't kno I had anxiety at the time).
I experience similar symptoms too you , with the shortness of breath , the twitching and racing heart etc , but there are manyo other symptoms you'll experience too , such as left arm , neck and back/shoulder blade pain and experiencing that WITH all those other symptoms like the chest pain and shortness of breathe you're a 100% that your gonna die no matter if the both the hospital and doctors tell you there's nothing to give them evidence there's anything physically wrong and it really is anxiety.
Me out of all people realize how scary it is and how it can keep us worrying and thinking the worst 24/7 that we are gonna die , but even though how bizarre out symptoms are it will NOT result in death , otherwise we would have died the first time experiencing those symptoms , yes it's hard not to freak about it but TRY remember that we are not going to have a heart attack OR stop breathing even though it sure as hell feels like it.
REMEMBER it's NOT going to kill us , many of us Experiance these symptoms , you're not the only one out there mate. I hope this helps , cheers