Could you explain what is decompression syndrome?

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.