Howdy,
I think these feelings are instinctive. Maybe things we recognize and don't know why. I think there is, for a while, a indiscernible smell of death. Not a stink of rotting flesh. Not something we consciously recognize but something our instincts alert us to.
I was sent to check on a boy who reportedly had fallen off a bluff. In reality his step father had shot him to death ,his sister and his mother also after strangling the neighbor lady with her pantyhose.
There was no stink or hum of flies, just a heavy sense of dread. The "Creeps" so to speak. It took away the urgency to get to the boy and replaced it with a bit of caution.
Another example I have is the movie JURASSIC PARK when T-Rex made his appearance and howled out from the darkness in the movie and standing water shook in the puddles, I had the instinctive urge to jump up and run from the theater. The hair on the back of my neck stood up and I was somehow telling myself not to be gobbled up. How far back does that go?
Thanks
Mike