I don't like the dark side, I hate to see all the beauty I create when I'm 'high' dribble through the impotent hands of the dark periods. But I've come to accept that this is how I am and always will be.
My only way out of the hole is to try and steer clear of addictions and learn new stuff.
Since I can't do anything of practical use during this period - nothing is exciting, the world is going to hell, I'm a failure and cannot do it, etc, I use the time to learn new stuff, read books on every possible subject and just try not to be too big of a drag on those around me.
I've been here multiple times and I know that each 'down' period is followed by a rush of energy and creativity and I have to be prepared with knowledge and health so that I can apply it during my 'mental spring'. This is how I've created great stuff before and I will in the future. At least this is my hope.
At the moment, learning lisp is a kind of psychotherapy that I apply to myself and it seems to be working, even though I have no idea what to do with that knowledge, it will soon all make sense.