As my fitness improves, I have moments where I "space out" on some climbs that had felt arduous a week or so prior. I get to the top, and then I realize that there was no involvement mentally, almost a sensation of waking up.
The visual perception of the hills will change as my fitness improves also. They just don't look as steep or long as before. I "space out" because I no longer have the same (real and/or perceived) physical exertion that I once associated with that particular climb, if I maintain the same prior speed of course.
It is a little pleasurable indicator that my fitness is improving. My internal dialogue is like, "I didn't even remember coming up this hill!" Of course I did, but I didn't at the same time. Good stuff.