Experiencing any life-threatening event can cause PTSD, and it can develop over time in firefighters, soldiers, and other first responders. The human body automatically responds to a perceived threat with the fight or flight response. However when the threat is gone, the stress response system should turn off. This is not true for people who develop PTSD. This program explains that the symptoms of PTSD are comprised of clusters including intrusive thoughts, reexperiencing, and hypervigilance. Part of the "Talk It Out" series.
Good video. I recommend for high school classes.