Dick York's back injury happened in 1959 when he was filming the film "They Came To Cordura" with Gary Cooper. It was the second last day of shooting and Dick and Gary were doing a scene pulling a trolley car carrying several men. Something went wrong and when one of the other cast members suddenly let go of the handle, Dick was left holding the weight of about 180 pounds. This caused all the muscles on the right side of his back to rip. Although he was in severe pain for days, apart from taking a few painkillers, Dick did not really worry too much about it at the time. His spine healed but incorrectly. Over the years the pain became worse and Dick literally depended on numerous painkillers everyday. It's believed that a combination of both is what caused his seizure on the set of Bewitched in 1969 which forced him to leave the series.
Over the years,the discs in Dick's spine slowly crumbled. It is said that he also shrank from his 6'1" frame to 5'10" and was almost totally hunched before becoming bed-ridden in later years.