I think the closest proximity to suan/sour is just sore. I like the suan metaphore, like something marinated/fermnated/drowning/gone slightly off in dull pain. It wierd because "sour" does feel very apt descriptor, English has sharp/stabbing/throbbing/burning/shooting/stinging/tingling/numbing... etc lots of metaphores. But "sour" is just your default sore/ache.