Sudden throwing back and forth of the head, usually from a car crash
Not all whiplash injuries come from car crashes, for example a sudden accident on a trampoline of on the football field can also produce the mechanics that cause this class of injury. The main problem is that the weight of the head, about 5kg, causes the neck to overstretch because it keeps going after the body is stopped. Secondary injury can then occur in the other direction because of the elastic recoil of the tissues on the neck. What is particularly interesting about whiplash injuries is that they can start of with relatively little pain, no pain in some cases, and then days later can gradually become horribly painful. So we generally recommend getting checked out as soon as possible after a whiplash event, even if it is not painful.
Treatment involves soft tissue massage, heat, mobilisation and manipulation. Dry needling is often used in these cases because the muscles become so dysfunctional and reactive. Soft collars are given in really nasty cases, but these are generally not used as the studies have shown them to be unhelpful in most cases.