PTSD, or post-traumatic stress disorder, is a mental health diagnosis, identifying a mental illness. Both the National Center for PTSD and The American Psychiatric Association defines it being exposed to an extreme stressor or traumatic event to which they responded with fear, helplessness, or horror, and experiencing four distinct types of symptoms related to the traumatic event/stressor.
People get PTSD after a traumatic event or series of events. War veterans were the first group studied around PTSD before it was even a formal and recognized disorder. This was because of the commonly gruesome traumatic experience of being in a war.
One way to think of PTSD is when someone’s “fight or flight” response is in overdrive, making it hard for the logical part of our brain to calm down our bodies.