Pain
They say one of the golden rules of writing is to write about what you know. I know about quite a few things but the one that I know the best is pain. Not physical pain, this is all in your head.
It is the kind of pain that starts off as a whisper in your mind, at first you can ignore it but after awhile you can't help but listen.
"Your so stupid, you never do anything right" it hisses in your ear and because you don't know any better you believe it. As your sense of self gets weaker the pain grows stronger. It goes from whispering to shouting.
"Your always going to be a loser! Always!" its not alone anymore, every single one of your insecurities has its own voice now and they are a chorus of put downs and hateful words.
The pain starts to creep deeper inside you. you lose the ability to feel anything. Your not sad, your just numb. Your brain is dead and although it sounds impossible it really is true.
You don't do much of anything anymore, what's the point? the voices are louder then the real world now. Your passion for the things you love is gone and all you want to do is lie in your bed and sleep.
If you could cry you would, if you could yell, scream, and hit your pain away you'd do that. Nothing seems to work though, the world has gone gray and as far as you can see that is how it will always be.
What happens next is up to you and whether your willing to fight against the voices, sometimes you'll be able to put back the colour in your world. Sometimes it won't work and you'll have to stay there for a bit longer.
It will work eventually, you'll wake up and see the blues, and the greens, and the bright yellows of the world. You'll take a deep breath and there will be no voice in your head but your own telling you that you won.
You'll feel happiness and hope again and oh, what a glorious day it will be. You just have to wade through the gray to reach the rainbow at the end.