Ah, yes, volume matters. I probably should have said "breath twice as much" not "twice as fast" but the rest still stands. And you probably breathe twice as much when you are walking than when you are at rest because moderate excercise (stationary bike) makes you breathe about thrice as much.

I'm curious about nighttime vs daytime breathing. I was under the impression that sleeping person breaths deeper than resting person. At least you can tell the exact moment somebody falls asleep because they start to breath deeply and loudly.