Or it is severely bruised. It happened when I was sparring with my Taekwondo trainer. I got too close and he threw a side kick, I dodged his sidekick my sidestepping towards his back, but he somehow bent his knee and spun a kick with his heel straight into my ribs. Now I am in some serious pain. Though like the idiot that I am, I am refusing to go to a doctor.
But hey, things have to break before they become stronger.