Well, I would say that I make friends with a large percentage of people who have at least a little PTSD from something in their past. I have only one friend with a mental health diagnosis that I know of, but I really believe that it's hard to go through life without being affected by direct or indirect trauma, mentally ill or strange family members, etc. But I can see how two very seriously ill PTSD'ers who trigger each other could not sustain a friendship without alot of patience, forgiveness, therapy, time out, and talking honestly. It sure would be a draining learning experience. Hopefully, true friends can talk openly about what is bothering them, and not do the silent treatment, or ask one friend not to tell another why she is mad and giving the silent treatment!