It's Mystery Spot (and a few other comments about how Sam really is much more like his father then Dean is) that really makes me think this is just Sam's way of dealing with all the events that have happened.But we have yet to see Sam experience strong emotions. From hate to love, ect
Sam acts as if he can't feel anything--literally. He's numb, like his emotions are completely turned off. It's Sam all right. He's not possessed and he's not altered. He's detached and empty. That's what's got me hooked. Even the prostitute fits in with the characterization. You pay prostitutes to leave when it's over. It's fascinating and it has me hooked. The monsters of the week are secondary.
It figures that this was a Ben Edlund episode. I always seem to love his stuff. Didn't he create the cold, alternate Sam of "Mystery Spot"?
And why I don't think anything sinister is happening with Sam.
But the previews for the up coming episode seem to really throw cold water on that idea. Unless its just in the course of a case (or in the solo hunting Sam did) dean finds out some activity that Sam did that Dean just can't get his mind around.
And clearly Dean knows Sam is willing (since season 3 at the very least) to do things that Dean absolutely wouldn't (or wouldn't at the time).
THough I assume Dean doesn't know what Sam was like in Mystery Spot or what he was willing to do. I also assume that Dean might not know that Sam killed that demon, when the host was active (though really Dean would have just killed her with the knife, no real question about that).
But he does know several things, that Sam is willing to do things that Dean just doesn't natural consider right.