Achilles tendon hurts soo bad?!?

a few days ago i was just hanging out at my friends house and out of nowhere my achilles tendon (or something in that area) starts hurting. it didnt seem anything major but i did nothing that day to make it like that, we just walked around. i did have gymnastics the day before if that might have anything to do with it. later that day i could barely walk on that foot it hurt so bad! then i had to go to gymnastics and i managed to do the usual stuff but it still hurt like heck. what could have happened?