One thing I'm correcting now that caused imbalance and some sinking in my stroke is actually related to breathing.
Some time you think you are turning your head properly toward the (back) right or (back) left and you are not... Your neck an head makes a unecessary motion before the chin and mouth really rotates right (and back).
Something like be rising and tilting toward the right before the head actual rotation and chin elevations (actually driving the upper part of the head down where it should have stayed).
It is unconscious, at least it was for me, Some triathletes seems to do it in an exaggerate manner for sighting (either build the move on the same unconscious bad habit).
I'm not sure my description is clear, the issue is mostly gone for me (completely on the left, while it comes back to haunt me on the right) but it create a MASSiVE imbalance and it also shorten CONSIDERABLY the time you have for breathing. That parasitic (reflex?) movement take a lot more time than a simple rotation (driven by the chin) toward the right (and slightly back), I would 2 or 3 times more (+massive imbalance).
Like most parasitic movement you have no idea it is happening and you think you are doing right.