I find in most anything I do, if you have a habit of not doing something, exaggerate doing it in training. Then, in a real fight (or hard sparring), when you're not thinking about it you'll do it normally.
Example: I have a bad habit when shooting at the range (rifles or pistol) sometimes of not breathing in between shots; this leads to rushing my shots, blurry vision (from not breathing), rapid pulse, breathing in the middle of a shot...all resulting in bullets hitting around the target. When I sense I'm doing this, I'll start exaggerating my breathing. I'll inhale and exhale, almost as is gasping for air, enough that I can obviously tell even while wearing protective earmuffs.
When I did rifle drill as a recruit on Parris Island, we always exaggerated movements when practicing, since people tend to "under-do" it in practice. Get used to over-doing it, and you'll tend to do it normally, whatever it is.
Same thing in sparring, sorta: I used to drop my hands. My instructor's solution: grab the lapels of my dobak, or the shoulder straps of my chestgaurd, when sparring. Forcing you chin into your chest also help[s squelch the bad-- and common-- habit of presenting your chin to an opponent in a way that says "Punch this really hard!"
Try exaggerating your breathing for a bit and see if it helps.
