>I also notice that I sometimes don't take a breath (or feel any need to) for several seconds, if I'm being sedentary.

Normal adult breathing rate is 12-20 per minute. So by the pigeonhole principle, if you don't pause breathing for several seconds when idle, then you're breathing too fast than what's considered normal. Your wife is hyperventilating, which could be a sign of stress, or a compensatory reaction to metabolic acidosis.