What is PTSD? It's a mental disorder, not a disability. Like many of your "invisible" disorders, it is defined in the "Diagnostic and Statistic Manual of Mental Disorders". This document, which contains zero statistics, is created by the American Psychiatric Association. The "disorders" are decided upon by a vote of the quorum. There is no science, no scientific study, nothing else behind the declaration of a "disorder". Homosexuality was a disorder until it became socially acceptable to be homosexual. The APA is all about prescribing medication for your disorder ... they offer no cure and no treatment outside of medication.
You might have a problem (disorder) but the answer is not medication nor is it preferential treatment by society.