It could be argued that Ron Kovic first started to show symptoms of PTSD at the Memorial Parade. What starts out as a day where he thinks he will be feeling better about himself and will feel reinvigorated as a result of being cheered as a war veteran turns out to be a highly negative experience for him.
After the car parade where he sees so many look at him in pity rather than respect, he sits up on a stage and listens to an older war veteran give a highly patriotic speech in support of the Vietnam War. Kovic is then called upon to speak, and at this point he shows signs of Post Traumatic Stress Disorder. The website www.betterhealth defines PTSD as:
Post-traumatic stress disorder (PTSD) is a set of mental health reactions that can develop in people who have experienced or witnessed an event that threatens their life or safety (or others around them) and leads to feelings of intense fear, helplessness or horror.
In Kovic this is triggered when he hears a baby cry in the audience before him. He means to speak in support of the war, "Our boys are doing it hard over there", but the baby crying in the crowd reminds him of his time in Vietnam, specifically when he entered a village with his unit and attacked civilians including families. Suddenly he is hit by flashbacks and in symptoms typical of PTSD, he is seized with panic, fear and a sense of helplessness. The audience can only watch in embarrassed silence and eventually he is quietly removed from being the centre of attention.
Kovic's reaction to Parade Day is really the start of a journey which seems him turn fully away from being an American patriot to being an aggressive anti-war campaigner - perhaps as catharsis for all the anguish PTSD brings to him.