Ever see a movie, documentary etc that the network logo is flashed on screen at the moment of peak drama?
That is done because the mind is most susceptible to impressions when it is emotionalized, stressed etc.
PTSD is related to that mechanism and is essentially a hypnosis based disorder
Hypnotists know they can access the subconscious when a subject's controlling, judgement factors are suspended.
Shock a person and they can have their link to conscious awareness ruptured - allowing impressions under the intellect.
Those impressions can take control of thought and feelings - make people re-experience things they don't want.
Those are flashbacks and they are resurfacing to burn-off but as people keep overreacting to them they reinforce.
Many studies show "trauma counseling" can make people worse because it has people refocus on things that need defocusing.
Concentration also has hypnotic aspects
This group (run by former military) has done a lot for PTSD sufferers
Patriot Outreach - Confidential, private and effective support for anxiety, daily stress, and even P.T.S.D. Supporting all Military Service Men, Women, Retirees, Veterans, Government Civilians, Battlefield Contractors and their Families.
www.patriotoutreach.org