I was the same i was so sure there was something wrong with me.
My doctors were very good i explained i thought it may be panic attacks and the thought of something wrong with my heart eas making it worse.
They were great i did an ECG and a tred Mill test, on the tred mill i completed the standard that a piolet of a Boing 747 has to pass so nope no problem there.
Was i convinced nope i was still sure something was wrong.

Just took time and a few good spells. If each attack was a heart attack i would be dead 100 times over

. Ask for a tred mill test it can help