When you need to relax in such a situation, don't worry about the breathing, just try and extend the time between breathing in and out, without trying, meaning don't hold your breat, try to do it subconciously. My Kung Fu teacher taught me that at 15 years old. DDuring a Heart Stress test, I told my Cardiologist I could slow my heart down, he said, "Show me', 5 minutes later, he said "Stop!", "Jesus I'm trying to stress you're heart out and you're going the wrong direction". Afterwards, he asked me what technique I used, I explained it to him. He is still my Cardiologist and always remembers my name, and has time for me.