Nonexistance
I don't get scared by the little things. At least, that's what I've always told myself. Heights aren't a problem, people ask me to kill bugs, and I'm always relaxed in the dark. What terrifies me, is the idea that none of it will matter-life that is. I'm scared out of my mind that in a few decades I'll pass away, and all that will be left of me are the stories I've shared, the memories others have of me, and a pile of rotting bones. Even then, I could fade from that existence. My friends and family will die, my bones will turn to dust, and any and all records of me could be shoved into a bleak black corner of the internet.
I used to think that immortality could only be achieved through a great historical feat; that if i did something great enough my name would carry through the centuries like Aristotle, or Julius Caesar. But in the grand scheme of things, even they will be forgotten. Humanity as a species has a finite amount of time to exist before we all die. Once we are all gone, any evidence of my existence will be lost forever. All my posterity will be gone; the records and stories I create will be lost; and like my bones everything else will turn to dust. That is what terrifies me. It's not that I will die, or even that i won't be remembered by everyone. But to lose all evidence of your existence, for it to look like you were never alive is the worst fate imaginable. I means that everything I've ever done or will do will be for nothing.