The bends is a syndrome caused by the rapid evolution of nitrogen gas bubbles from body fluids when an individual moves too quickly from a higher-pressure atmosphere to a lower-pressure atmosphere. It can develop in both divers and fliers. Fluids in the vicinity of large joints are especially susceptible to bubbling, which causes severe, sometimes incapacitating, pain in those areas. Other symptoms include nausea and abdominal pain; in severe cases, coma and death result. This happens because the amount of a gas that can dissolve in liquids is directly proportional to the amount and duration of pressure. Scuba divers therefore surface gradually to normal atmospheric pressure; otherwise nitrogen bubbles form in body fluids in a manner analogous to the fizzing that occurs when a bottle of carbonated beverage is uncapped. Caisson workers and others who spend long periods in high-pressure environments return to normal pressure in decompression chambers at staged intervals that may take hours, and experimental dives to real or simulated depths of several hundred meters require a return period lasting days.