The action of having nitrogen dioxide in the blood caused by rising to the surface too quickly. Animals know instinctively how deep they are able to dive or stay down; Man dives with artificial aids - air and weights. Then in panic or foolishness he rises to the surface from 100 metres too quickly. Then decompression chambers are needed to clear the blood.
Tha answer by ginbottle is misleading.
Nitrogen Dioxide has nothing to do with the bends (Decompression sickness). Which is caused by release of Nitrogen which has been absorbed into body tissues under pressure.
Diving mammals dive on a single breath which means there is a limited amount of nitrogen to be absorbed and eliminated by body tissues and a limited amount of time for the gas to be absorbed.
Humans can suffer from the bends when ascending too rapidly from depths much shallower than 100 metres , particularly if they have been breathing compressed air for longer periods than recommended on tables available to divers.
I was watching a show on whales and they said that it's a mystery as to exactly how they avoid the bends. Obviously, something in their body conteracts this effect. We, however, aren't sea mammals and are out of our element that far underwater.