Hi OP, I am no stranger to HA as my Dh has it.
When you say that you don't think it is anxiety related, how does that work if you have health anxiety? Health anxiety IS anxiety, and it is a devious, pervasive and convincing problem. It rarely allows us to look at statistics and how things really add up.
You mention Anaemia and previous blood loss, which is much more likely, along with anxiety, to cause symptoms such as this. If you have been suffering from stress for some time, both of these things will have a cumulative effect that kicks in later, which will include fatigue, breathlessness and chest tension.
Heart failure at 42 would either be congenital (born with it, so you'd already know) or extremely unlucky. It is very, very unlikely, even if you had high (or very low) blood pressure.
Even with a first degree relative who was diagnosed with heart disease below the age of 55, you would still be highly unlikely to have it at your age.
I am 50, and my dad was diagnosed with angina at my age.
It bothers me only when I have a 'symptom'.
If you are a regular at your gp's, take heart and try to relax a little, at least mentally.
I am sending you all the best, and I hope that you can find a level ground with your fears.