Hey Pete, welcome congrats on making it 53 days so far! Unfortunately as you're learning it's not as easy as just quitting having life be grand. THere's more difficulties behind it. I was hit badly by anxiety as well. I'm still not for certain if it was a result of the quit, and resulting changed brain chemistry, or if I used tobacco to mask anxiety issues I already had didn't realize. I suspect a bit of both.
It doesn't hit every guy, sometimes the reaction is a more physical one with the fog being worse, but anxiety (and depression for that matter) is not uncommon when quitting, you are by no means the only . I'd only made it a couple weeks in before my first near complete meltdown, I know well what you mean about your mind racing a mile a minute. It took me a while to realize understand what was happening and a bit longer to realize this can be a normal side effect of quitting. If you find you don't respond well on xanax, go back to your doc try something else. Lexapro worked wonders for me (I'm still on it with 660 days in).
Lots of guys try different ones depending on what works best brain chemistry isn't an easy thing even for your doc. I'll PM you my number. Text if you need anything.