Damn, I remember watching that on TV back in the day and being a little freaked out by it. I don't recall thinking anything was wrong with him though, he was just way too good at selling injuries and other people's moves. People also thought he may have been genuinely injured by those nasty chair shots from Edge at Wrestlemania 21, but the pain he was in there turned out to be brilliant selling on his part, too (well, I'm sure they DID actually hurt, but not to the extent where his shoulder was injured in the way he made it seem. I think there was even a dirt-sheet report on it in the days following.)
Then again, knowing how he turned out only two years later and knowing that sort of mental deterioration (from various concussions and hits to the head and whatnot) had to have happened over a long period of time...