You probably tense up, and that's why you sink! Good to know you can at least swim on your back, that does count as swimming! I never advanced to more complex strokes of swimming because I refused to breathe when they wanted me to - I don't think they had any clue of an asthmatic kid's aversion to anything blocking breathe when needed, and the fact that summer time is always the worst time for my allergies. I'll breathe when *I* need to breathe, thanks! I am fine underwater as well, can swim for a long time any way, just let me breathe at my own pace!