It basically boiled down to (in his case) "so your heart is beating fast? that's ok. not a big deal."
It is always amazing to watch an expert in any field distill a seemingly complex problem into a simple one with a simple solution (at least in my son's case).
Obviously, his decades of expertise was able to eliminate a world of root-cause possibilities and guide the conversation to help my son believe this simple conclusion.
He'd also induce panic attacks by having him breathe through a narrow straw. Probably helped to demystify them and practice dealing with them.
Or does your son have to do ongoing treatment like meditation / prescription medication?