re: Is sadness stronger than happiness
Burst of laughter over a joke is not a manifestation of happiness but a short term pleasure, the ability of a human being to laugh over a joke lies in its novelty, removing which will remove element of pleasure.
We have an innate ability to adapt happiness or incidents of happiness quickly, on the other hand sorrow or perception of loss have many stages, many people are lost between denial and depression and never reach the stage where they can accept it.