Use it or lose it totally makes sense. When I got my very first symptoms in 2016, I remember walking was the only thing I felt compelled to do. Anxiety reliving as @turnitaround says and good VRT. A short time later, I began to feel fatigued on a regular basis and also triggered by the walking, let alone any cardio exercise (I went for a gentle jog one morning before work, like I used to do before all this, and had to call in sick). Too much of a walk now seems to make me feel worse, or at least I feel like I then need a long sit down. In March I did around 13k steps per day as part of ‘walk all over cancer’ as I wanted to start getting back into exercise. I wonder whether it’s a coincidence that at the end of that month I went down hill drastically and very fast and still very gradually regaining a bit of normality now (and not walking much).
Feels totally bewildering to think that exercise would help me and yet it’s the one thing my VM has consistently prevented me from doing! Hmmm, do I just need to push through? Graded exposure etc? Very very gradual, in my case maybe.