This irrational anxiety has it's roots in the inability to be confident enough (in oneself) to discern the difference between a simple benign symptom v a serious one. In this situation common sense and the ability to 'hold still' flies out the window and panic ensues. HA then sees danger/death around every corner and views the world as an unsafe place.
HA is usually a learned/conditioned way of responding so it's familiar. More often than not it also has it's roots in an individuals upbringing ie a troubled parent (had similar issues) or a significant traumatic event in a young life.
Recognising where the anxiety (and the pattern of responding) comes from the is the first step, then reprogramming your self beliefs (and your way of responding) is the next and it's the hardest part.
Many of us with HA issues can't do it alone, many need professional help usually from a psychologist. Many of us know what to do but don't know how to do it. We need to learn how to have the inner confidence to respond to health adversity in a more rational, calm appropriate way and to feel safe while we are doing it.
Our human bodies don't run to clockwork and we can't always control what happens to them. They are ever changing in a myriad of ways and most of these changes are quite harmless, they're just blips along the way.
I hope in a small way that this will help