Piers the whole point is that you DON'T think about the breathing. You just sing. That's why the car is a good place, precisely because you're doing something more important, and you're NOT concentrating on the singing. That's what combs out all the tangles and fixes the song in you brain. That's why it's better than sitting in a room with the words in front of you. You're accessing the automatic areas. Works for tunes too. Just hum them and next time you go to play - bingo.