Headless Corps nightmare

I had a nightmare about a headless body that entered my room and started looking at my books on my bookshelf. The thing is I felt as if I weren't sleeping at all but I couldn't move. Now I understand about sleep paralysis but I just want to know what this headless corps mean and why do I always feel so scared. I also had a dream about just hearing the voice a young teenage girl singing in my ear in Latin and want to know what that means. Please help me with these questions.