Barotrauma is an injury caused by pressure change in a cavity, and is a common fatality among divers. An example of such injury is to the middle ear or sinuses.
Equalising is importantMore about pressure
On ascent, the reverse will follow, with gas inside the cavity needing to escape with the decrease in external pressure. The gas will bubble out of the Eustachian tube spontaneously. A diver can assist the process by simply swallowing, also known as 'popping the ears'.
The human body is designed to withstand an average 6.7kg per 6,5 square centimetres, the pressure at sea level. If the same area of water and air were compared, water weighs far more than air does. Therefore, water pressure on your body is far higher than the equivalent to that of air pressure.