Sometime between shaking Henriksen's hand and lying down on the cushy-soft bed at the Wagon Trail Motel, it hits Sam. So much is over.
Not just having to evade the FBI, though that's no small relief. He's finally free of those horrible doubts, those nasty little thoughts that creep in when he's hip-deep in books, wondering if there's any way to keep Dean from dying, trying to quash the feeling that he's going to have to unleash his Antichrist powers and pull Dean out in his own harrowing of hell, after Dean's suffered too much.
Ruby would never have proposed her plan if he had any demon in him at all. He breathes a sigh of relief. He's ready to sleep for a week.
But then there's a knock on the door and Ruby comes waltzing in, the little devil on his shoulder and always the bearer of bad news.