Laughing is enjoyable, for that reason people search for things that amuse them. Touch is pleasing, therefore the massage business thrives. These things can become addictive due to the pleasurable effect that they produce. People have been exercising obsessively for a long time but only recently was an idea postulated as an explanation.
Laughter often begets laughter and in large doses, has the ability to make one feel high.
It is said that with drugs your first high is the best and never able to be duplicated. What keeps people using drugs, despite the downfalls associated with use, is that eternal quest for that ethereal feeling that they experienced the very first time. Pleasurable activities, like exercising, sex, laughter, touch, etc. can all become dangerously addictive. Exercise, sex, laughter, and touch all produce positive effects within the body via chemicals in the brain. These chemicals are called endorphins, a mixture of the two words endogenous, meaning from within the body, and morphine, a powerful pain fighting drug that is also used and abused for recreational purposes.