Have you ever felt it? What brought it on?
A real probability of death brings fear.
The thing is, probabilities can be masked and manipulated.
For example, a child can easily be traumatized by fears of death, because the child is actually unaware of how real the probability is. To a child, even a far semblance of death may seem close-at-hand, which is the reason why they can become so scared at what adults see as “harmless”.
I once got stoned and went down a river in a canoe. We were supposed to get picked up at this certain place on the river, but as it turned out, that place was at a different river altogether. It got really dark, so I couldn’t even see my friend at the other end of the canoe. It had been raining for 3 or 4 days so the river was going really fast. We ran into a full grown like major tree that had fallen into the river covering 3/4 of its width. It took us about an hour to get untangled from that tree and secure the canoe. I was bruised from the top of my head to the bottoms of my feet and had a bit of water in my lungs that I kept puking out as I got the canoe from between these two major branches. The only things we took were a bowl, a sack, my car keys and cell phone and two paddles and a hat. When we got out of that river all we had was one paddle and the hat. Pretty crazy shit man.
I have felt it numerous times, I would say lack of control is the reason far more thatn fear of death. When a situations spins out of your control it can bring fear on in order to jump start you into some sort of defensive action or reaction.