Forget downward dog. I'm signing up for laughter yoga. It's the goofiest exercise I've ever done, and you leave feeling GREAT.
Laughter is a practice, just like anything. As the participants of this class show, you don't need to be going through happy times to laugh. Quite the reverse: laughing gets you through the hard times.
I laughed every time I listened to this tape as I was editing. I hope it has the same effect for you!