Very sorry to hear about your loss. That really sucks! It sounds like your cool side temperatures were definitely on the low side, but your hot side temperatures sound fine. As others have already said, any guesses we could make would only be speculation, but you almost have to give serious consideration to the mice you fed him on the day of his death for him to have suddenly regurgitated and simply die like that... I don't know if there are parasites that can kill a snake that fast, which the mice could have had? Could the mice have still been alive when he swallowed them and they caused internal injuries? I've never heard of that happening, but maybe some of these other guys have...