If you are cutting a small piece of drywall and you don't want the cut piece to fall into the wall (or on your head if it's on the ceiling), here's a trick you can use. Before you start the cut, take a corkscrew for opening wine bottles, and screw it into the drywall in the center of your cut. Then when you make your cut, you have something to hold onto (the corkscrew) to keep the drywall piece from falling once it is freed.