The science behind decompression sickness?

Question

How exactly does gas inside you cause pain, in significantly reduced, or increased pressurized areas??? And is nitrogen always the case or could it even be oxygen??

Answer 1

As the pressure increases, small bubbles of nitrogen are compressed to the point that they leak out of your tissues into your bloodstream.  As pressure increases again (for example if you are coming up from scuba diving), the bubbles expand.  They are now too big to escape your blood stream.  They often get trapped in joints or elsewhere in the bloodstream and the blocked circulation causes excruciating pain.  Oxygen molecules are too large to behave this way and are almost always bonded to other molecules anyway.