What causes laughter?
The majority of researchers believe it has to do with relief to the flight or fight system and related to human bonding. 

For example, we hear the phrase "laughter is contagious". That's because we want to let others know we have good feelings towards them and would like to connect at some level but in a quick and non-direct way.

However, for situations where the joke may be "dangerous", Suslov's theory is better understood. I have also personally witnessed it many times. This kind of laughter follows the familiar model: "Oh no, I hope he doesn't say something that pokes fun or embarrasses me in this social setting". Next, you hear the joke and realizing it doesn't embarrass you (too much) the relief and release of energy transmutes into a laugh.

Also see: http://en.wikipedia.org/wiki/Laughter#Causes

Reference: 
How Laughter Works:
http://science.howstuffworks.com/environmental/life/inside-the-mind/emotions/laughter.htm