I can't remember if this was one story or a series. The story I'm thinking of takes place preseries, while Sam is at Stanford. Dean had been paralyzed and using a wheelchair either since birth or since the fire. At some point, some supernatural creature healed him, and he's struggling to adjust. I remember a scene where he has to climb stairs and finds it incredibly difficult, and any sensation below the waist is overwhelming, since he's never had feeling there before. He goes to see Sam at school and Sam assumes at first that he's a demon/shapeshifter.

Hope this sounds familiar to someone; I'd really like to re-read it.

Thanks!