The short of it (or "abstract" as we like to call it once we have more than 15 years of schooling) is that your brain has a limited multitasking ability and the 6 first hours after a learning experience is vital to the formation of memories. Thus, if you have a traumatic experience you can hinder the formation of the kind memories that will provide you with neverending flashbacks simply by keeping your mind occupied on other stuff the first six hours after the traumatic experience. The study shows that your memory will not be affected, only the rate of flashbacks you will receive from your now damaged brain.
So to conclude the 'abstract' while you're waiting in the emergency room (or whatnot) don't mull over what happened, there will be plenty of time for that later, but engage your mind with a visiospatialstimulant like tetris (or whatever game like it you have on your cellphone). Your life will be better for it.
If you are interested in more on this you can check the whole article on plos one an open access, peer reviewed, international online publication. The study is done by Emily A. Holmes, Ella L. James, Thomas Coode-Bate and Catherine Deeprose at the Department of Psyciatry @ Oxford University. The study is based on two previous findings: 1. Cognitive science suggests that the brain has selective resources with limited capacity and 2. The neurobiology of memory suggests a 6-hour window to disrupt memory consolidation.