I've posted earlier about Sam again losing his grip on reality, and now Jared gives some more details on just how crazy Sam will get, plus how Dean reacts while also having to deal with Castiel's return.
Jared said that Sam will no longer be able to hide his visions from Dean, which will lead to Sam being institutionalized:
"Sam thinks he's trying to protect Dean from the knowledge that he's in pain. He's going 'No, it doesn't hurt, I'm fine,' while he knows he's dying. It's going to get so bad he can't hide it from anybody. He'll be checked into an asylum where they think he's fully crazy, and honestly, he is. He kind of has been for a long time."
This will lead to lasting effects for Sam, who Jared said will get a wicked case of insomnia:
"There's an episode that we're talking about right now where Sam isn't sleeping. The longest anybody's ever gone without sleep is like nine days, and they died, because your organs shut down. I wanted to make sure that we don't have an episode where Sam hasn't slept in a week, and he's losing his mind, and then he suddenly gets it together and helps save the day. I want him to be human, and I want him to be effed up. What's made these characters likable is that they are human."
Sam's trip to the asylum will occur in the same episode as Cas's return, giving Dean a lot to deal with all at once:
"I think with Dean, it's really hard for him to deal with Castiel's betrayal. We've seen Sam wrestle with visions of Lucifer, and now it's Dean's turn to have that kind of a story. We'll see Dean struggle to wrap his head around the Castiel issue. He's like, 'How do we forgive this guy? How do we trust him? That's how we got hurt; that's how we got burned.' Dean's once bitten, twice shy. We'll see him wrestle with some of his own demons."
Supernatural returns with all-new episodes on February 3.