Why is writing so relaxing...

Recently I have taken up writing, mind you I'm not very good at it so don't expect any books out of me in the near future. ;) I doubt they would like smiley faces in books anyhow. Ok, Ok, I'm drifting way off topic. Back to my writing... Whenever I'm stressed out over something [or someone] I write. Sometimes for a couple hours. The strangest part about it is, I'm writing about the very thing that is stressing me out - and it makes me feel BETTER. I would love to have an explanation for this phenomenon. It really does not seem like it would make any sense, after all why would writing all your thoughts down about something that is bothering you help? I'm not going to dig too deep for an answer - all I know is it's working, & I'm sticking with it! The power of the pen, or keyboard in my case... ;)