Lawler used a pile driver. The move gives the appearance of being dropped on your head. If properly executed, no harm will result. If improperly executed, serious injury and even death can result.
Lawler and Kaufman practiced this routine in the gym, of course.
The late Owen Hart nearly ended the career of "Stone Cold" Steve Austin when he improperly executed a pile driver on Austin. As I recall, Austin sustained what the wrestlers call a "stinger", and was out of action for quite a while after that match.