I am not an expert, but can only repeat what I was told myself by a therapist when I suffered post traumatic stress disorder.
Mine was caused by being the victim of several armed robberies when I worked at a Credit Union, the last one 10years ago, when one of the armed bandits walked among us, as we laid on the floor. He was pointing his gun at us and saying "now, which one of you am I going to kill".
As you say Fiona, when we are faced with our own mortality, it can leave a life long scar on us.
Therapy taught me to accept that what I was going through was normal. I was not crazy, I was not the only one experiencing such symptoms.
The other thing it taught me was the ability to survive. That even though I was fronted with a life threatening moment, I did survive.
Just like you did David.
The best thing David, is to accept that the trauma you suffered was real, and the lasting nightmares are normal, very unpleasant, but normal. What a terrible thing to go through as a youngster. But you suvived mate, thank goodness.