People who are diagnosed with PTSD are most commonly not directly suffering from the Trauma itself (Trauma with big T), but instead it's defined as a combination of many small trauma's (small t) exploding when confronted with a big Trauma. 

BIG Trauma

Car accidents are quite common - unfortunately. Whomever has experienced an accident before, or even witnessed from the outside, gets startled and involved in Trauma. Just a week ago, on 20th of January, a huge bus-accident occured in Verona, Italy. 16 Fatalities, 26 major injuries. Even just hearing gets you stopped in action for a moment. The bus was loaded with kids. Do your emotions start to grow? They were from the same country as you are. Are you genuinely hit by this accident by now? 

Natural reaction in such a case is to feel greatly sad, it might feel as if you have to cope with this as being an actual victim of the Trauma. Even when there is no relationship whatsoever to any of the real victims, and you have not witnessed it yourself. It just gets you startled. You put your Facebook profile picture pitch-black. Out of sympathy.

So, what with the small t's? What are those? For me, these are things which happened in my youth, during my development into an adult, any memories from being a toddler to today - all adds up. These small trauma's were sever at the moments they happened, but easily 'forgotten' through time. Think about getting some beating from relatives, being diminished by others, bullying, anything which only makes you feel sad for a  moment, but then gets replaced by actions and other - more important things. 

At the moment of collision, observing the tremendous amount of damage occured, I felt: HELPLESS, RESPONSIBLE, ANGER.  After a score of therapies and tests, it turned these emotions are actually linked to my childhood. And THAT's when it becomes interesting...