I'm going to be getting ANOTHER mouth guard because I clench/grate/grind my teeth and now have jaw problems.

I'd really suggest either learning how to breathe before bed (meditatively?) or relenting and getting a mouth guard (and perhaps doing whatever necessary to deal with anxiety/discomfort of that). Not all mouth guards are horribly big... if you really needed one, they could always make a lighter one to be worn during the day you could wear at night. better safe than sorry!

see if you can deal with the anxiety somehow and it should help. my dentist also 'prescribed' me Advil to deal with the inflammation/pain of the jaw/mouth clenching... so thats also an idea if you need one.