Is it okay to be 18 and afraid of the dark?

I am 18 years old and have this almost irrational fear of the dark. I know that there is nothing there but I always feel as if there is something that is going to get me. I can watch horror movies and scary movies (it is my favorite movie genre) without any trouble and I never feel as if things from the movies are in my room so I don’t think it has to do with that. My dad doesn’t think it is anything, that it is something in my head but I’m also wondering if it is nyctophobia (irrational fear of the dark). Sometimes at night, I have to run to get into my bed because I’m afraid something will grab me from under my bed and sometimes I have to pull my blanket over my head and I’m scared that if I take it off, there will be someone looking at me. My question is: is it okay for someone my age to be afraid of the dark? Also my 20 year old friend has the exact same problem and she wants answers as well.