A: It almost certainly isn't your fault. When someone hits you from behind, it is virtually always the other driver’s fault. The basic rules of the road require drivers to stay far enough behind you to safely stop their cars if you stop, even if you stop quickly. If the driver behind you cannot stop his car, he is not driving as safely as he needs to be. Sometimes both you and the car behind you will be hit by a third car. In that case, it is almost always the fault of the third driver for pushing the second car into you. Your attorney would be in touch with the third driver's insurance company if that happened.
In rare instances, if you stop in an unsafe manner, you may be liable. An example of this could be if you missed your turn and stopped suddenly in a travel lane.