Whiplash is the common term used for a hyperextension injury to the neck. Though the neck is a very flexible structure, it can be injured when the weight of the head exceeds the neck's ability to control its motion. The injury usually happens when the head is suddenly jerked back and forth beyond its normal limits during a car accident, rough contact sports, or a fall. This jerking motion can cause over-stretching and tearing of the neck muscles and ligaments and can cause the discs between the neck vertebrae to bulge, tear or rupture.