...some of them from being a physical performer (being a drummer is pretty much an athletic activity), and some from advancing age. Collins also had at least one back surgery which was botched, as I recall; he also has some neuropathy from type II diabetes. I really feel for the guy...for some of us musically-inclined kids in the '80s, he was one of our heroes. I remember being blown away by some of the experimental, pioneering production techniques that Collins and Peter Gabriel employed on all those amazing records (and let's also not forget the contributions made by producer/engineer Hugh Padgham).
And yes, it's a terminally-overplayed song now, but I still remember how listening to "In the Air Tonight" for the first time was absolutely terrifying--in a good way, like a horror movie. You just knew something bad was coming, and yet when those drums kicked in, it was still shocking--it sounded like the end of the world. Listen to that one again with fresh ears sometime, and take note of all the little things going on in the mix, long before the Drums of Doom blow the walls down. That kind of musical drama is what inspired me to study music seriously as a young person, even when a lot of my peers didn't consider such pursuits "hip".