At approx 11:15a on Jan 31, a temp emp reptd to our HR Mgr that after his shift on Fri, Jan 28 he stepped off the stairs & felt a ?pop? in his neck. He didn't report it to supervisor as there was no pain. Upon awakening Sat, Jan 29 he had a stiff neck. He felt better Sun. On Mon, Jan 31, approx 3-1/2 hours into his shift, the pain & stiff neck returned.