I thought I was getting better

For the past two months I’ve been some of the most confident I’ve ever been. My GF and I have been going at it like rabbits. 2-4 times daily at points. I’ve felt unstoppable and powerful.

Three days ago, I lost my erection during foreplay and haven’t gotten it back since. I barely feel anything, and what is worse, I’ve gone into a full scale panic.

My GF is very supportive, but I’m so embarrassed and mortified. I’m petrified of sex right now

That’s awesome you’ve been able to have good sex multiple times daily for awhile! Congrats! Try focusing on all the good times you’ve had, don’t let one minor setback take you back. I know it’s hard not to spiral, but you’ve got this! Try some meditations, they help me relax a bit. Good luck!

I’ve been there before, sometimes the periods where it isn’t a problem make the times when it is so much worse, because you feel like you’ve overcome something just to “fail” again.
It sucks and it’s embarrassing to talk about but I think just trying to explain to your GF where your mind is at can help her help you through those moments and odds are she really wants to if she cares about your mental wellbeing.
Just knowing it’s not a disappointment to her can help re-spark the fire in the moment, revert back to foreplay or even fore-foreplay, whatever works for the 2 of you.