EMPLOYEE WAS ENGAGED IN HIS REGULAR JOB STACKING 50 LB BAGS ON PALLET. HE PLACED A BAG ON PALLET, FELT A POP IN HIS BACK AND SOME PAIN. HE DID NOT THINK IT WAS ANYTHING TO WORRY ABOUT AND FINISHED HIS SHIFT. HE REPORTED THE INCIDENT ABOUT A HALF-HOUR AFTER IT OCCURRED BUT DID NOT DECIDE TO SEE A DOCTOR UNTIL MONDAY, DEC 12TH.