Perhaps Sam seemed more relaxed because he didn't freak out about things. He didn't really have strong emotions one way or another. He was just here. If anything, this place was an improvement because at least Dean hadn't found out about his lack of a soul and so wasn't trying to find a way to stuff that hopelessly damaged soul back in him.
"Just a week," Sam confirmed with a nod. "Any advice? This place is more than a little crazy."