One of the biggest mysteries to me is that small slice of time right after McLoophole and Sayid had their confrontation. Whatever was said/done to Sayid changed him. I'm starting to think that McLoophole exposed Sayid to the other timeline, showing him what he wanted--Nadia was alive. Sayid came to terms with the fact that the island timeline wasn't real, and eventually he'd shift there.
Desmond's behavior is what hit me. "What's the point in being afraid?" Dez has seen the other side and suddenly enters this "zen" state...as if he no longer cares about the island timeline. Likewise, Sayid has issues with emotion/caring/etc. It's possible that they both have seen the other timeline and have 'checked out' so to speak. Their behavior is eerily similar.
It's a stark contrast to the other timeline, where the characters are getting excited when they get flashes from the island timeline.