Wow, it is actually so ironic that you mention the second part in your head as being a shadow. I'm a somewhat spiritual person, I mean I don't really go to church and stuff, but I do believe in God and the spirit world. I watched this haunting program on TV once that was about a boy who went with his mother, a ghost-hunter, to a graveyard one night. Once there, they saw a bunch of shadows running around and one caught up with the boy and he said he could feel it entering him. They went home and nothing happened for a while, but as time went on he said there was this voice in his head telling him how worthless he was and the mother said that the boy changed. He was arrogant, didn't go to school anymore, and became a shell of his former self, stopping all his hobbies and interests, but also becoming a nasty, snickering child and backchatting his mom. He also threw something at his mom once, missing her head narrowly. A man came over to their house and realized the boy was possessed by a shadow demon, as the boy also said he heard voices in his head. They proceeded to cast it out with a priest and the demon revealed its name as "irritum" which is latin for "nothingness/emptiness". That was one of the things they noticed, he was void of all emotions most of the time.

I was struck deep when I watched this, this was describing so well how I am feeling, so empty and void of feelings. I don't really hear a voice, but I think thoughts of being useless and pointless as a person. I also walk around in public like a shadow person, walking behind trees, normally wearing a hoodie, covering my face somewhat, looking down so people don't look at my face. This is just the most terrible thing to go through, this depression, and it feels like it never wants to leave.