I know exactly what you're talking about. I was very fit in my twenties, then got badly injured and sort of got very unfit for about ~7 ish years where my focus changed. I recently got back into mountain biking, and the first few hill climbs were confronting to say the least. Literally me lying on the ground holding my chest, and ego thinking "What the actual f--k". The real motivator was having dropped kinda large cash on a new bike. I didn't want to let myself down and quit. If the op has a similar vocation, I'd lean into that stuff. gently, gently of course.