Gi'day Gas tech --- PTSD -- such a biggie. PTSD can be caused by a brain trauma (as per a single event head injury, or repeated events, or severe alcoholism/drug abuse, or from concussive blasts in a war zone), or from any life experience that causes abnormal distress.
If you've managed to rule out permanent brain trauma through MRI scans or CAT scans its a simple matter (if the word simple there can even be used) of going over the traumatic events until it becomes another non-traumatic life experience, almost viewed through the eyes/memory of another younger version of yourself, and not yourself as you now are (or will be).
If, on the other hand, you have yet to rule out brain trauma, the journey becomes a lot harder (sorry) and will come with many trips and falls along the way .. but it is still a journey worth going through and eventually you will discover your own unique version of peace of mind that will be different to anyone else's version, simply because yours is a unique story captured within your neural net/brain/thoughts.
Just know that others have walked that same path -- and are still here, living life.