I toss and turn too much to sleep with a weapon to trust I won't hurt myself or my fiance in my sleep. But I have weapons stashed around our house at strategic locations. I don't notice them anymore when I see them, but when we first moved in, it was a real comfort to have them. I was taught growing up to always have a weapon handy, and I always have. Even before the PTSD. So, I don't know. Personally, I think that you have larger fish to fry right now and if it helps you sleep, then it helps you sleep. My teddy bear does the same for me right now. I feel like an infant, but my cats and fiance aren't going to judge me.
However, I suggest that if you do get a dog (and dogs are AWESOME for PTSD, just look at all the threads), I would put it somewhere out of reach for the safety of you and your dog. One or the other, not both. And I'll be honest with you, if I thought my cats could stand a dog, I would SO have one right now. I never felt safer at home than when I was living with my dad's dog.