I always knew that when I'm not in a good mood, my body language suffers. I've also always felt that changing your body and environment can change your mood. Often, when I don't feel like going out, I'll take a shower, get dressed really well, etc. and eventually my mind changes. I just came across this video that shows experimentally, that simply changing your own posture for just minutes can change the levels of hormones in your body and your mood:

http://www.youtube.com/watch?v=Ks-_Mh1QhMc

The speaker shows you five "power" poses that have this effect. I'm sure there are more. This was all really fascinating to me, and is only 20 minutes long. The stuff on poses and experimental results start at about 10 minutes into the video.