Nitrous Oxide is sometimes used to prepare divers for deep dives. As a side effect of the pressure of deep diving, nitrogen is concentrated in the bloodstream. Most people are familiar with the bends, which occur when a diver is brought to the surface too quickly, allowing the nitrogen to bubble in the blood, instead of gradually allowing it to permeate back into the tissues. This concentration of free nitrogen is coupled with increased oxygen and nitrogen inhalation.
When you dive to a hundred feet, you are at an effective three atmospheres. These atmospheres of pressure reduce the volume of the air in your mask, same as pistons reduce the volume of air in your car's engine. But because your lungs are a fixed volume, you wind up breathing more air per breath than you would at one atmosphere. This increased quantity of nitrogen and oxygen produce the same effect as hyperventilation, known in this case as nitrogen narcosis or the Rapture of the Deep.
To prepare divers for this effect, instructors recomend that divers try nitrous. Nitrous produces the same sort of giddy disorientation and silliness in a controlled environment.