Annihilator

I'm scratching a picture on the wall
Of a man called nothing at all
Why are they keeping me here
Please just let me go
Please let me go
I'm hearing voices deep inside my head
But I don't want to listen
Why don't you leave me, just leave me alone
Cause I'm in no condition
Join us - I won't follow you
Join us - there's nothing you can do
Join us - you're never going to win
Join us - cause I’ll never let you in
What are these creatures crawling over me?