What is this decompression sickness?

Usually from diving: It is the body's response to reduction of pressure without equilibration. Usually associated with too rapid ascent from depth, it is also called caisson's disease because of the air pressure necessary to keep water excluded in contruction (e.g., deep bridge abuttments).

DCS: Decompression sickness (dcs) is also called the bends. When a diver descends in the water- pressure increases. As the diver ascends there is less pressure which allows dissolved gas to form bubbles in body tissues. This can cause a variety of different symptoms ; in some cases can lead to death. It could also occur in an unpressurized aircraft going to high altitude, if a halo parachutist does not.