How about keep the job, but volunteer in a quiet sleepy little oxfam store, something like that?
I worked in a big brutal supermarket with anxiety for 4.5 years and wouldn't recommend it even to someone without anxiety, let alone with.
It's a difficult one because no one knows how you are, how your workplace is. Retail is a very varied landscape.
My advice would be keep the job for the moment, have a think, go see the doctor, join a self help group and may try mixing it up exercise, mindfulness before shifts.