[crusty]

[quote=
and crusty, are you saying if i pack hard enough on the surface (for example untill i feel the pain) and i dive and comeback up, air can get trapped and cause barotrauma?[/QUOTE]

As far as i understand it can cause Barotruma.
The likelyhood of it happening is low but it can happen.
If you do dive deep the pressure of the surrounding water will compress the air in your lungs completly and allow your lungs to squeeze together.
If you look at pictures of free divers at depth you will see their chest is compressed.
As you ascend the air in you lungs expands and if you have a section of lung that is not expanding properly ( tissue may be stuck together) the lagre amount of expanding air you have packed inot you lungs has to go some where and may cause barotrauma.
There is also a problem with the avolie ( not spelt correctly) but i cant remember what it is.

If you need more info try Efettah, Eric is a full book on this sort of stuff.
Or Sebastian Murrat i did his free dive course and became aware of it there.

Crusty