Laughter question

What exactly happens in your body when you laugh? What are the physiological changes that take place? Do these changes last longer than when you cry? What happens when you laugh so hard that you cry? I am sure that it is not the same as crying when you are sad? Is there a technical name for the study of laughter?

The physiological study of laughter is known as “gelotology”.

Cecil briefly indicates how laughter works here.

A somewhat more comprehensive discussion is here. and even better here.