I too get those periods of harsh breathing and feeling like the pain is so overwhelming that I am going to pass out. After much testing to rule out anything my Dr. and I decided that it is anxiety. I take ativan for it when it comes up quick like that. It helps get mme calmed down and get my breathing under control, then i can deal with the pain.
Lack of oxygen in the blood actually will increase pain, or at least make you less able to cope with it.
Just my opinion.
Tracy