Maybe not trauma related at all, for me, but curious as to whether other people have experienced this. (I suppose I'm a bit fascinated by sleep anomalies and dreams, as they give a glimpse into that evasive unconscious mind.) You wake up from a "loud" "BANG!" and a sensation of having been hit on the head, but can't remember a dream relating to it, and haven't experienced such a thing in waking life. It's happened to me at least twice.