My scariest moments are when I get really bad divemasters. I mostly try to control my buoyancy with my lungs instead of filling and dumping air in my bcd. When I first started diving, it took me a little bit longer to fine tune my buoyancy this way than it does now. And the %#@# divemaster would come over and inflate my bcd, causing me to go into an uncontrolled ascent because I had problems dumping the air.