WAY back in the day I knew a guy who was in the cargo hold of a 737 cooling off on a hot day after unloading the bags. He nodded off and woke up halfway to Tampa. He might have snuck out if the rampers at TPA had mercy on him, but the big dummy banged on the ceiling and scared the passengers. There is no way out of there, he was stuck until landing, banging or no banging. He was fired on the spot and had to find his own way home when they landed.
* this was considered funny, but it might not have been if there had been dry-ice cargo in there.