I too have popped a rib out for no reason. Oh, I may have coughed or sneezed or some other normal everyday thing, but it seems silly to hurt yourself just doing that. The last time I popped my rib out I was recovering from surgery and post surgery infection, so you know I wasn't up running around or doing anything to make a rib pop out. Luckily, my insurance covered my chiro appt. Dang, he propped me up against a wall and made me bend my knees and learn this way and that way and then, wham! He threw my into this padded wall. It popped the rib back in place, but geez, how violent.
Good luck to you. I hope you rib goes back where it's supposed to go and does it quickly. I know how painful they can be!