What is diving and the bends?

As a diver descends to the undersea world, the weight of all that water exerts tremendous pressure on his or her body—nearly 15 pounds per square inch for every 33 feet of depth.
It would be impossible to inflate the lungs under such force if not for the high- pressure air delivered from a scuba tank, which counteracts surrounding pressure.
These inhaled, pressurized gases are pushed in higher-than-usual concentrations into the bloodstream, much the way carbon dioxide is forced into water under high pressure to create soda water.
If the diver rises too quickly to the surface, it's like uncapping a seltzer bottle.
A sudden drop in ambient pressure lets gases come out of solution too rapidly, forming bubbles in the diver's bloodstream.
These bubbles, particularly of nitrogen gas, can create the painful and potentially lethal condition known as the bends.
To prevent this problem, also called decompression sickness, diver's ascend gradually and sometimes pause before surfacing in order to give their bodies time to release nitrogen gas slowly.