The science behind that feel-good feeling it isn’t all that complex. The human body releases endorphins in the act of laughter, and those endorphins relieve stress. It is a natural physiological response. Turns out, the body has no way of knowing if your laughter is genuine, or if you’re a big faker.
A study done way back in 2003 documented its participants' emotional state after 60 seconds of "real" laughter and then compared it to 60 seconds of "faked" laughter. Turns out that both kinds of laughter have the same affect on the body. Check it out: http://www.theage.com.au/articles/2003/03/31/1048962698891.html
So… If the human body has no way of knowing if the laughter is genuine you can reap all the same benefits by faking it. Fake laughter turns into real laughter in my Laughter Yoga class all the time. Go ahead, just try it.