My conscious

Why is it every time I look in a mirror is see someone behind me but when I look behind I see nothing. It is the strangest thing to see some one behind you in a mirror and feel someone behind you but no one is there. Maybe it my conscious, maybe it my eyes, but what ever it is it is creeping me out I told my therapist but I think she is just trying to make me feel better ( Its just your conscious you will get used to it ). Imagine being so scared you tell your therapist and it is so insane they think you are lying. Yeah, not good. I started to ignore it but eventually it started following me but I ignored the signs ... not a good choice because now am watching my own funeral and saying hi to my dead mom.