People sometimes assume they must be blocking out traumatic memories if they're involved in a serious accident -- like a car crash -- and they can't remember the wreck itself. They may even find that they can't remember what happened after it, even though witnesses tell them that they were awake.
While there are cases where people block out memories, some experts have found that the brain's survival mode may often be to blame. When this kicks in, the brain operates at a higher level of awareness, aimed at increasing your mental and physical abilities so that you survive.
However, since it can only do so much, the brain has to give something up to increase survival functions. What is often surrendered is the ability to make memories. So, it could be that you're not blocking out the memories at all; your brain just didn't make them when the accident was happening, leaving a gap until it knew you were going to survive and switched back to its normal mode.
Some people have linked this to the well-known flight-or-fight syndrome. There is an influx of adrenaline and your body gets ready to physically work to preserve itself -- either by fighting to stay alive or by running from the threat. While the classic flight-or-fight response may not be fully useful in a car accident, it is still triggered in the brain and the change in function may keep you alive.
Have you been in a serious crash that you can't even remember? The road to recovery could be long, difficult, and expensive, and you must know what rights you have to compensation.
Source: Smithsonian Magazine, "Why Can’t Accident Victims Remember What Happened to Them?," Rachel Nuwer, accessed March 23, 2017