I can say from the early days of having the 1st years of panic anxiety, that my heart was also very fast, and I was often russed of to hospital by ambulances a few times, and the answers have always been the same as the answers your getting its anxiety. I was even in spain once and had it and was put into hospital with whats called tachiacardia however you spell it. I can only say that this will calm down, and adding what if thinking will not help, so tell yourself its just a trick of the nervous system nothing more, theres no need to be afraid, dont let them fool you any longer. Do some relaxation and it will go away once your body gets to the level of lowering your anxiety levels. Stop the ''what if'' stinking thinking. All the best.

Bless you.