I know my experience is far away from what you are facing but if it helps its worth trying. Many years ago, when I was getting into mountainbiking I was experiencing something similar. I wanted to go on the bicycle it was a great feeling relaxing after a nice two hour ride, but we live at sea level, and the nice paths start uphill. I was not in shape at all, I remember going with my brother one day and having to turn around after 10 minutes as I was struggling trying to follow him, and it was not even uphill yet!
Through the years, I have gained much more shape, but it always stresses me to think I have to start my ride going uphill for a while. The days I just go, the satisfaction feeling is huge, not just for the excercise, but also for being able to beat my mind.
Its a long process, and I imagine yours is even harder, but it is worth the effort as you improve with every try. And if part of the reward is showing smallsteps, that is the biggest reward I can imagine.
This is a great image for me - thanks! This is what I am hoping will build over time, where I am able to start reading "uphill", but then enjoy once I am on the fun trails of the book :)