I've experienced episodes like you describe. My therapist called them "in between PTSD and Panic Attacks". They were not classic panic attacks, but had elements of them, and were definitely PTSD driven.

For me, those intense fear floods are connected to my anxiety challenges. At times they will feel like pure adrenaline rushing through me. I usually don't have the fear of being killed for much longer than a few moments, if at all, unless it is sleep/nightmare connected.

But even a few moments of fearing that I will be harmed or killed is too much, awhile back I went through a cycle where I would suddenly feel a rush of stark fear and terror, and I would be sure for just a few seconds or so that I was about to be harmed violently. I was able to talk myself down each time, I also took them to mean that I needed to pay attention to something. Usually that I was too stressed out and needed to return to basics: sleeping well, good food, water, fun activities, etc.

Sarah