I understand this fear, or I wouldn't frequent this board.
This is like putting your life on hold in anticipation of a catastrophe that might never happen. Any one if us could get that dreaded diagnosis at some point in our lives, but we cannot predict when or how. It is part of the great unknowable, and this is precisely what anxiety feeds on - the unknown. Anxiety is already a living death. We don't need a diagnosis to accept it, we are already living it here and now. It may not kill us in an instant, nor require a thousand rounds of chemo, but it pretty much annihilates our life force, we're a dead man walking already.
It seems contradictory to survival to halt living in fear of what may never happen. Even if we think we have the symptoms of this deathly disease, we have no medical context to judge it correctly, all we see is the word 'cancer' and our mind leaps ahead straight to the terminal countdown.
To me, HA is the very worst of the mental terrors, because we can never escape the thing that terrifies us so much - the body itself. We can't avoid it (like flying, swimming) or remove it (like a spider). We can't hide from it (like thunder, trains, elevators) or tell ourselves it can't ever happen (cos it can, sadly). We are stuck with our body, for good or ill. I can only see acceptance of that very uncertainty that we fear as the way to beat HA. We need to accept that we can get unwell, that we are one day going to die (we're doing it right now, slowly!). With most people, they get on with their lives, seeing death as this vague, far away certainty that doesn't interfere with the present, but with HA we have it up against us every minute of our lives. We are THAT close to it every single day. This is a really bad way to live, a wasteful way to live, and it is best to find a way to treat the anxiety first, because for each day we give to this thing, it's another day wasted.
And you know, none of us have any real idea how we'd react to a terminal diagnosis.
None of us.
We can run it through our minds until we pass out from fear, but we will never really know until it happens. And often, we react very differently to how we imagined. I can vouch for that.
Nobody wants a terminal diagnosis, not HA sufferers or anyone else.
I suppose it's like living in terror of being hit by falling masonry - it is not worth ruminating over, but it COULD happen, couldn't it?