More than 100 people were injured when the ship was battered by force 11 winds and lost propulsion off the north-west coast of Spain on 4 November.
Shortly after 13:30 GMT, Gilks arrived in the ship’s main deck living room, pushing his wife in a wheelchair, the MAIB said.
At about 17:10, the ship “rolled violently”, toppling his armchair backwards, causing him to hit his neck on the floor.
In severe pain, he was helped back into his chair by a nurse, the report said.
Four hours later, he was fitted with a neck collar and X-rayed, but the lack of a side X-ray hampered diagnosis, and he was not placed on a spinal board, it added.