Welcome to Wrong Planet. Human beings are much more complex then most people understand. One reason is that we have multiple brains. One exist on the left side of our skull and the other on the right side. We incorporate multiple beings inside us. They become our daytime brain and our night time brain. The night time brain is active during REM and deep NREM sleep. These day/night brains are very different from each other, like night and day.
But because humans are complex creations, we are designed to come back to life. If the dominant brain that exist on the left side of our skull dies, our supporting brain, our night time brain can come online and fill the void. This is what happened to me when I was a young child of 3 or 4. I was attacked by a large animal and died, but I came back to life. I stood next to my body and watched my parents in utter horror standing next to my body, my dead body, which they placed on my bed. I didn't know I had died. I was just a very young boy trying to figure things out. Then a voice spoke to me. It said, "live or die, chose".
If you look deeply into near death experiences, you may find something of interest.