I sometimes forget to breathe when i'm awake. i don't notice until i begin making noticeable sounds and it happens most often when i'm concentrating.

Breathing automatics: You should not have to think to breath. If you have episodes of not breathing spontaneously you may have a problem with the control center for breathing in your brain. You should see a neurologist and get a Sleep Study.

Breathing: Breathing is an involuntary process and one doesn't stop breathing unless there is an abnormality of the respiratory center and it's pathways. Therefore you shouldn't have to force yourself to breathe. It will happen naturally. However if you focus on your breathing and become mindful of it you will interrupt its natural rhythm and it will seem abnormal to you. Try to take your mind off of it.