When I was a kid, I heard that the sun is going to eventually explode, destroying planet Earth and us all. This was deeply saddening for me on a deep level, I remember crying and all.
My parents tried explaining this will take 5 billion years, and we will all be long dead anyway but this wasn't really helping. Prior to that I had a major shock when I learned about death, and this was kind of a relapse.
Looking at it now, I think doomerism, preppers, apocalyptic religions and the guy that stands on the street shouting "it's the end of the world" are all a basic part of the human experience. It's not a coincidence every cult eventually reaches the narrative of the impending end of the world.
Death is suppressed and finds other avenues to pop out in