So as you all know, you have the helicopter scene right in the beginning, and then have it again later in the game. The second time though, Walker makes the comment:
Wait, this isnt right. Its like we did this already.
Now after I finished the game and nothing was made of this comment, I figured it was just a bit of comedy for the player to chuckle at. But when I heard him say that, I thought that maybe we were actually in Walker's nightmare where he is reliving the horrors of Dubai over and over again, especially since they talked about PTSD throughout the game. I think I like that idea better than the one they actually did, because I still dont understand it fully.