I am talking about breath hold induced hypoxic state. Basically at what point during such an exercise would you expect the risk of fainting to be significant or can it happen at any saturation level? Can I assume, that at 50% the danger of fainting is very high, like 90% and at 70% saturation it is extremely low? Is it possible to train to be able to withstand lower saturation levels and not faint? For example would an experienced breath holder be able to not faint at 40% saturation? And finally, if you regularly do breath holding exercises, would you expect your red blood cell count to rise, similar to altitude exposure?