I could swear I have built all of those in Spore at some point.

You should watch out because nitric oxide is highly explosive. About the same as nitroglycerin. No but seriously: While it is true that nitric oxide is released in the nasal cavity (always not just during buteyko), the amounts are waay to low to have any noticeable impact. If you are doing breathing exercises any visual effects you notive are probably coming from too much oxygen.

Just don’t eat anything. For three days you should be fine. If your stomach hurts just drink water.