I get this, in fact I believe that all writers understand this, it’s definitely a kind of therapy, when you’re sad, mad or have been just plain bad, that’s the time you should write. Your emotions are hightened and writing will bring you back to feeling normal (Whatever your normal is) and calm you down.
I know if I’m feeling sad or angry and I write it out then the world seems a better place, it will cause your writing to take on an edge and different way of thinking and that could be put to good use on your next character in your book. Even if you don’t write books put your feelings down in letter form and get it out of your system. I promise you’ll feel better. You can say all the things that you wouldn’t say to someone’s face and it gets it out of your head.
Writing for therapy is an all round winner.