I had a similar situation when I got caught in an ankle lock. I herd a loud pop but it didn't really hurt. By the next day my ankle was the size of a softball. I went to the doctor per request of my wife.(a nurse) and after x rays was told I had a bad ankle sprain. It didn't really feel like a sprained ankle but it heeled up fine after a couple of weeks. It has never gave me any trouble since. However remember in a bjj. class there is nothing to prove, so tapping out might not be such a bad idea.