"There is another symptom of acute trauma that can be easily missed if you are not on the lookout for it that strongly predicts the development of later PTSD. In layman's parlance, we might call it "being spaced out." More technically, we call it dissociation. When people dissociate, things come apart in a variety of ways. Often they feel separated from themselves, as if they are watching themselves from some outside vantage point. Frequently they feel that there is some type of invisible wall between themselves and the rest of the world. Sometimes they will feel that everything in the world, including themselves, is somehow unreal. I've heard patients describe this experience as being like looking at the world through the wrong end of a telescope, so that everything seems smaller and distorted. In extreme instances, people so thoroughly lose track of things that they develop amnesia."