One last bit of theory for tonight, and then I'll stop spamming y'all
That red eyes flashback thing Dean has a couple times in 4.01? Listen to the noise. Sounds like combat, right? People screaming? Dean's eyes looking around? Like watching motion, things moving quickly around him.
I have the BIGGEST feeling that part of the reason Dean doesn't remember hell is that it wasn't just Castiel who went to get him. There was, like an angel strike team or something, and there was a big Angels vs Demons smackdown to get Dean out and Castiel is the only survivor. And right now, Dean can on no level accept that a) angels exist and b) angels died to free him from Hell.
*twitch*
THIS SEASON IS GOING TO FRIGGING ROCK!!!!!