The Beast Within

He dwells in the deep dark corridors of my soul
The beast will never let me go
His demeanor is as black as coal
Of this I truly know.

The beast within
Hidden from others
They never know of his sin
His trail he always covers.

The beast within called pain
He smiles at my loss
On me he surely makes his claim
He makes me play his dreadful game.

He wants to swallow me whole
Possess me mind, body, and soul
While he laughs from his horrid knoll
He thinks he is good at taking his dreadful toll.

The beast resides within me
Fight, I do try
I wish he would let me be
What possesses him to do this? Please tell me why.