My mom has PTSD related to childhood abuse. She was treated with a combination of traditional talk therapy and a heavy drug cocktail, and the combination was really devastating. She went from a person with issues to psychosis in the course of her treatment, and it took her years to recover from that treatment. Having seen that, if I had to choose a treatment for PTSD, I would try EMDR or some kind of cognitive behavioral therapy. The thing that has been most helpful for my mom, is to lead a MUCH lower stress life style (took early retirement, cut off many family members) and anxiety meds as needed.
In terms of your child, there may be both nurture and nature at work. You child may be mimicking, but he/she may also (like day) be more susceptible to stress than most people. In my family, in addition to several people with PTSD, we also have people with addition issues, anxiety, one family member has broken heart syndrome, and we all have high blood pressure and other physical manifestations of stress (even though we are generally a thin, active, healthy bunch). Your child may need some proactive help to deal with stress, beyond any specific issues with dad.