Hi there and thanks for posting this question. I am sorry to hear about your very uncomfortable experience. In regards to your question it is extremely unlikely that your brain experienced a lack of oxygen due to compression of your tummy. In other words we don't only breathe through our nostrils (nose) but also we have a very powerful muscle called the diaphragm. The diaphragm separates the thoracic cavity (heart, lungs & ribs) from the abdominal cavity and performs an important function in respiration. A diaphragm in anatomy can refer to other flat structures such as the urogenital diaphragm or pelvic diaphragm, but "the diaphragm" generally refers to the thoracic diaphragm. You can see a picture here "http://en.wikipedia.org/wiki/Thoracic_diaphragm
According to Chief Dina Knight Cerebral hypoxia
Cerebral hypoxia technically means a lack of oxygen supply to the outer part of the brain, an area called the cerebral hemisphere. However, the term is more typically used to refer to a lack of oxygen supply to the entire brain.
keep reading here http://dinaknight.com/is-your-brain-power-being-limited.html
So as you can see although it is really unlikely that you suffered brain damage you should really check with your doctor. In addition you should have seen some serious symptoms blurry vision, loss of consciouness or similar.