The Causes and Effects of Laughter

Everybody laughs, feel angry and feel sad, but I think that laughter is the best things of this three feelings. Then, what are the causes and effects of laughter? we should laugh when we see something funny such as movie. We should also laugh when we feel happy, for example, when we pass the exams. After laughing, we can feel happier than before. I watched Japanese TV show about health that laughing is good for our health. For example, if we laugh before we go to bed, we can sleep beter than without laughing. In Japan, there is a proverb which means that you can get happy if you laugh, so I want to keep laughing no matter what may come.