We all do it: fall.
So how do we fall safely?
On stage, there are a couple of integral rules to remember.
Keep you center of gravity low, and fall on the mushy bits. Don't aim to land on anything hard, like bones. Keep your hands up, because wrists can snap like toothpicks. Be spacially aware. For example, don't fall downstairs. Take a slight glance behind you, and really sell the fall. If you know you have to fall onstage, take a step behind you, plant your feet, and lower your behind. Roll on one side of your back, NOT your spine. Keep your neck tucked, and keep the momentum going. It is not about speed, it is about control and momentum. Finish the roll, and keep the flow.
If you get injured for whatever reason, notify a stage manager, and get an ice pack. Most likely, the adrenaline will dull the initial pain.
Most importantly, get back up!