I would encourage you to get the free Qigong eBook “Way of the Inner Smile” from http://www.healingdao.com/ (see top left of the page. You have to subscribe to their newsletter to get it). Very interesting. Here is a very short excerpt:

[…] The Tao sages in China are usually depicted as smiling. This is an Inner Smile, suggesting that no matter how bad the worldly burden becomes, the Tao within their inner heart will remain an eternal source of smiling joy. […] […] Smiling is energetically very different from laughing. “Laughter is the best medicine” the saying goes, and laughing certainly releases tension and is good for the body in a number of different ways. According to Chinese medicine, if someone laughs too frequently or too loudly they may have excess heart chi and are unconsciously trying to release it. Laughter is more of belly centered emotional release than smiling.

Smiling is more subtle than laughter, a more inward and more sustainable experience. Someone who smiles continuously is not considered in excess, assuming it is not a “phony” outer smile. Smiling is less about emotions, which are our response to outer life events, and more about subtle feeling. Inner Smiling cultivates this feeling to a high level, focusing on the spiritual joy that arises from our inner soul and radiates out as subtle presence.

Thanks to ancient Tao masters passing down their tradition for thousands of years, we now know the secret of the Inner Smile is hidden within our inner heart. The inner heart is not the physical heart, and it is not the emotional or feeling heart. There is a “third heart”, just as there is a “third eye”. This inner heart is a portal to direct experience of what is called “soul”, a concept in the West that has successfully eluded all definition.

The ancient enlightened masters gave us a very specific map of the Inner Smile’s pathway within our body. It arises like a wave from the inner ocean of our unknown and unborn self. Before it gently splashes onto the beach of the outer world, it passes through many subtle layers of body-mind consciousness that they mapped out in great detail. […]