Quote Originally Posted by Feytalist View Post
I believe he was weakened simply because of all the damage he had taken over the course of the book. The Mantle had shielded him from those effects, but not actually healed him (as was mentioned once or twice in the book). When he rejected it, all those injuries came rushing back. Including the broken back from Changes.
Yup, this is correct, he says so pretty clearly himself. The Mantle is allowing him to ignore his injuries and it healing them while the Mantle is on, but it's a kind of "temporary HP" sort of thing; the second the Mantle goes away, all that damage comes back to him.