Fitness!
I can really feel my fitness levels picking up. I used to only be able to run/jog very short distances before my chest would tighten and I would find it difficult to breath. I just went for a very short jog - about 2.5km - and had none of that. I would have gone for a second lap, except it was getting very dark and there are no lights along the trail.
This may not mean much, but it has occurred to me tonight that the tightening of my chest hasn’t been a problem recently, something that is big news for me!