I think its different for everyone. In Oct 04 Myself and My then 4 year old where diagnosed with PTSD after a car accident. WHen I was putting my boy in his car seat he jumped out and into front knocked the car out of park and as we were on top of a hill car flew backwards, child thrown around car, I was dragged by car along ground and through brick wall. Child afterwards was uninjured would you believe, by traumatised. However at counselling when we were looking at some of its issues it appeared he may well have had PTSD before the accident. I lived with his dad and his dad was verbally abusive, he was I believe on the verge of a breakdwon and screamed all day all night at me and I am not exagerating. During therapy it became apparant that this triggered the PSTD. Eventally with sandtray therapy, time love and help from child pshychologists child is doing ok but has taken a long time and a year later still some problems. My PTSD came from the guilt that I could not stop the accident occuring. Others I have known come from various things. I guess it depends how traumatic the event is to us. Some people have a huge accident but recover and everythings fine, others get PTSD. Hope this helps in some way good luck
M