Why?

I'm sitting at home, driving to get groceries,  sleeping (or sleeping at work.... don't tell my boss) and then the anxiety hits. Its not just that that little bit of anxiety. This is Fight or Flight "I feel like I'm gonna die" anxiety. Yes, in a large part it has to do with the fact that I have fairly PTSD but where does the rest come from? Seriously someone tell me. At those times when the anxiety from the PTSD hits and I feel like my mind is not my own it is the most terrifying thing I have ever felt. I try to be strong and trust that God has me go through this for a reason.  The problem is I feel like I'm at my breaking point. So my question tonight is why?