This is probably going to be a rare choice, but my biggest fear is probably time loops. It's genuinely chilling, the thought of being stuck in one moment for what could be the rest of your life. I saw a prank video once where they were making someone think they were trapped in a time loop, and I'm serious - I legit started CRYING, think about how scared that person must have been. You can't do or say anything to stop it. You just live the same thing, over and over again, until it drives you mad.
