I confess my actual feel-good addiction has become hula-hooping. I can do it in the warmth and precipitation-free, judgement-free zone formerly known as "my living room," it counts as cardio (internet says it might burn as much as 200 cals/hour), and really all you should try to do at once is 10 minute-bursts, especially to start. It's so easy to pick up the hoop and go for a few minutes. I am really glad I decided to pick it up. I find once I can get myself to do one thing, it's so much easier to get myself to do anything. For me, it's almost meditative. But running also helps. Though I'll be honest: running helps get out rage and frustration at least as much as it helps put me in a positive mood, so it's kind of 50/50 on that - really, anything that gets you moving, and exhausts you, tires out your mind as much as your body and really helps to break bad feedback loops.