Decompression sickness (DCS) occurs when the body is exposed to a sudden drop in surrounding pressure. DCS occurs most frequently during deep sea diving or when flying in a nonpressurized aircraft.

DCS is caused by the formation of gas bubbles in the blood and tissues. At normal altitudes, nitrogen and other gases are exhaled or dissolved in the blood and tissues. However, during severe changes in altitude and air pressure, nitrogen and other gases form gas bubbles. These bubbles block the flow of blood. This condition can be fatal if not treated quickly.