Sorry to hear what you're going through!
I've experienced a mild form of hyperventilation syndrome on/off all my life.
I'd feel like I've forgotten how to breathe, or like I'm constantly out of breath.
It would come and go and lasts for weeks/months when I'm feeling very anxious, which would further fuel the anxiety.
Do you do any sport?
What helped me understand that it's a product of anxiety, and that I simply have to live with it when it occurs, was taking up sport regularly.
There's something about exercise that just immediately reminds you you're a healthy person. You'll feel aches/pains/hyperventilation that are caused by physical exertion, and you'll notice how different it feels when it isn't anxiety-related.
Not saying that it's a cure-all, everyone is different! But I run three times a week now and it has worked wonders.
I wish you all the best in your recovery from the beast that is anxiety!