Theorically, yes, air floats up as bubbles underwater, still a lot of people can make it trapped in their nasal passages in any position underwater. I may have a reason not to believe this if one or two people said it out of 10000, but the truth is that I have seen it with my own eyes many times someone doing it. No bubbles left their noses, which means no water got in there as it'd extrude the air out of there. I am 29 yrs old now, until the age of 28 I didn't even know this could be done and never even thought about it, but after realizing how common it is even among people who can't even swim properly, then yeah... It bothers me not being able to do something so many others can do. It does not bother me in any other things, but it does in water related stuff coz you always wanna be better at something you like doing.