I think, well I think I think, that when Desmond fell off the ladder, he had a vision. He dreamed about his future. Then he woke up and everything felt like dejavu for him. He knows what is going to happen because of that dream that day. Oh, yeah I just confused myself. He would only know what happened in the dream then, wouldn't be able to adjust for things he changes like saving charlie from lightning and then the next time from drowning... He dreamed about the past after the hatch blew him nakedly through the jungle and knocked him out. So why does he continue to see the future? And his crazy flashback dream ended when he got hit in the head at the bar....