Realize, too, (and this sounds ridiculous as hell when you are getting depressed) that you cannot stop it, but you CAN grab onto it and let it take you (it will grab onto you regardless, just don't grasp back--it's not your friend and in time it will let go, but not as quickly if the claws of your mind are holding it close to yourself too). Try to accept it, let it come through you and then let it go when you can, as soon as you see an opening.

Don't forget your "toolbox" (your coping skills). They are important. And we are all here or you should you want to talk, vent, yell, whatever--but that's a given.