People with the highest susceptibility are those who suffer from fatigue, drowsiness, boredom, insomnia, and excessive contact with humorous scientific hyperbole. Although studied by institutions throughout the world, it still is not completely understood. Everyday people are unsuspecting agents, who 'infect' helpless individuals. There is no cure, and the only treatment is allowing the behavior to run its course. Pandiculation is the act of yawning and stretching, and it is highly communicable.
A common misconception is that pandiculation is brought on to increase oxygen levels in the blood and to reduce carbon dioxide, but scientific evidence has proven that theory unsound.
Dr. Robert Provine of the Psychonomic Society studied effects on college students who were given different types of gases (air is a gas, remember?) to breathe for 30-minute intervals. Using four gaseous concoctions, ranging from normal air to those with both extreme levels of oxygen and/or carbon dioxide, Dr. Provine detected no change in occurrences or duration of yawns. Subjects did tend to breathe a little faster in a low-oxygen atmosphere, but stopped short of looking like goldfish trying to breathe in bleach water. Provine also conducted the same experiments with subjects before, during and after exercise, with the same results.
So, what causes pandiculation, and why is it contagious? Dr. Provine believes it is due to evolutionary history, and is a response developed to coordinate the social behavior of early humans, yet remains as a vestigial response. Strangely, there is no pecking order when it comes to contagious pandiculation--it can be as infectious coming from an innocent child as from Federal Reserve Chairman Alan Greenspan, or balloon-busted country music crooner Dolly Parton.
In any case... experiencing a complete and satisfying pandiculation, without interruption, feels pretty good. Pass it on with impunity, and coordinate your own social behavior experiments.