Hi Roxy
The pattern of isolation seems to happen in different ways for a lot of sufferers, they will isolate from anyone or anything that they cannot control. I don't mean control in a bad way, more with friends and family they can see them or not, their decision. Interact with them how they want, friends they have know for a long time, may not know they have PTSD, as they have not been told, so less stress of them asking questions. With work if they have a job, can also be a kind of isolation, as in it is a different world where they can immerse themselves into it, using it as a tool of distraction from the pain in their minds.
Very close relatives and friends may be find they are ignored and not contacted, because of the stress of trying to explain how they feel and what is going on. Tough to understand, when you would think that close friends and family could help, there lies the problem sometimes, they are too close, and the sufferer does not want to share the pain, hence the isolation.
I hope that makes sense, and give you a bit more of an idea of how this can effect them.
Amethist