One thought is that he was shipped in the underbellie of the air craft, and if he wasn't shipped with a heat pack, he could have gotten real cold, because when the plan gets up to there high flying altitudes, it gets very cold down there that I have heard
If he wasn't packed in the box with stuffing to keep him from bouncing around.

You changed his habitat to something diffent than what he had been used to at your parents house.

Just some thought for you to think about.