No One
My worst fear is that I won't be needed anymore. That I won't matter to anyone for any reason. I dread having a few "friends" who only want my skills, or who just feel sorry for me and don't actually have a particular interest in my mind or interests.
One of my most vivid nightmares from childhood was coming home one day to find that my family didn't even know me; to them I was a stranger, coming to see the house they were selling, the house I'd grown up in. But they didn't know me, and I woke up crying from the feeling of loneliness, emptiness it gave me.
However unlikely it may seem to some, this fear is always present in my life. It drives me to excel at what I try to do, and fuels at least some of the disappointment I feel if I fall short. Even if I succeed in whatever I'm attempting, I fear that nobody notices, because I'm not important.
Whatever else happens to me, I wish never to be a no one.