One of my best friend's cousins actually went through something like this. He was on a plane that crashed, in Greece or Turkey, can't remember which. Anyway, he sent a text message to his mother saying things like, "the plane's going down and i want you to tell everyone that i love them", etc. It was on the news the following morning - at the time, they didn't know why the plane crashed. Apparently, the pilot's cabin lost pressure, but the main passenger cabin didn't. So the pilots were unconscious, locked in the control cabin, and the passengers were awake and literally waiting to die.
It's hideous to think about.