Don't be afraid to ask for help, especially here because we understand! Trauma is trauma, it doesn't matter if you got it from childhood abuse, witnessing an accident, military service, domestic violence or any other kind of trauma. None of us are 'better' than the others. I can't speak for everyone but I have 'good' days and 'bad' days. On good days I can get through my days without too much anxiety or second-guessing myself, on bad days I feel like I shouldn't even leave the house.
It is hard for friends to understand PTSD - sometimes you might be okay around them and communicating with them, but sometimes you might feel it's better to not 'burden' them. Do I think you burden your friends? Absolutely not. Do I feel like I burden mine? Yes, I do feel that way sometimes. Like when I tell my friends I *need* to leave a restaurant because of anxiety and they roll their eyes... I feel like I just ruin everything. I wonder why I bother trying to do things outside of my house at all. So I get the whole feeling like nuisance. I get the withdrawn thing and the isolation thing. It stinks. As do the bad dreams! I don't know about you but I seem to get them more after a stressful day.
I can't help you as far as what to do with yourself. But for me: if I'm not feeling going out and seeing friends, I am okay with staying home. I will catch up on books or tv, I might color or just do nothing at all! I give myself permission to NOT feel badly over something (PTSD) that I have no control over. I chalk it up to good days & bad days and I try to just get THROUGH days most of the time.