Suddenly dying without having left any instructions to how I want my remains to be taken care of.
Suddenly dying without having left instructions for the care of my cats, even though everyone knows I want them well taken care of and I'll haunt anyone who does otherwise.
Suddenly dying and no one noticing until my cats are starving. Not that I'd mind if they snack on my corpse, I just don't want them to get to that point.
Heights involving human construction. I don't trust it.
Having the Titanic (or other sunken boat and ship) raise itself underneath me while I'm swimming. I still don't know why I'm afraid of this.
The collapse of civilization leading to a Mad Max era. Or Waterworld. I don't know what would be worse.