Perhaps you should tell them it is a brain disorder and leave it at that? It truly is biological in nature, not simply a matter of being "nervous" or "high strung". Their brains are forever altered. On MRIs done of Evie's brain, you can see the PTSD in her hippocampus. It is very real. It is not unlike schizohophrenia, epilepsy or autism in that regard, although different areas of the brain are effected obviously.