i too have issues with yeast. god - 10 years i went with CONSTANT trouble. Drove me mad!
Anyway - the breathing thing. Yes you can forget to breathe (seems daft but it happens).
Another thing i catch myself doing is only taking tiny breaths. Once you're aware you're doing it you can catch yourself and put it right.
When you're breathing regularly, i fancy you're only taking air into the very top part of your lungs. You can tell if you take a few slow breaths... right down so that your tummy sticks out full of air.
and here's a useful night time thing for you. It's called 7/11 breathing. Breath in for the count of 7 - breath OUT for a count of 11. You'll be amazed the calming difference it makes.