Decompression sickness, also called the bends, is caused by nitrogen bubbles forming in the bloodstream and tissues of the body. The bubbles occur if you move from deep water towards the surface (where the surrounding pressure is lower) in too short a space of time.

Symptoms occur soon after the dive has finished and, in the most serious cases, it can lead to unconsciousness or death.

If you suspect decompression sickness, stop the dive, initiate first aid, and summon assistance from a specialist in divers' medicine. Treatment is 100 per cent oxygen on site and during transportation, followed by treatment in a decompression chamber.

The symptoms of decompression sickness vary because the nitrogen bubbles can form in different parts of the body.

The diver may complain of headache or vertigo, unusual tiredness or fatigue. He or she may have a rash, pain in one or more joints, tingling in the arms or legs, muscular weakness or paralysis. Less often, breathing difficulties, shock, unconsciousness or death may be seen.

The symptoms generally appear in a relatively short period after completing the dive. Almost 50 per cent of divers develop symptoms within the first hour after the dive, 90 per cent within six hours and 98 per cent within the first 24 hours.

In practice this means symptoms that appear more than 24 hours after the dive are probably not decompression sickness.

An exception is if the diver has travelled in an aircraft or has been travelling in the mountains. Under these circumstances, low pressure can still trigger decompression sickness more than 24 hours after the last dive. As a result, it is wise not to fly within 24 hours of a deep dive.