The term whiplash is a good description of what happens to the head and neck when the body and head move in opposite directions at the same time.
Have you ever seen (hopefully not done this yourself) an adult shaking a small child front to back vigorously? Guess what - whiplash. Often the child suffers but can't tell what's wrong. How about being pushed or falling forward or backward and then stopping abruptly by hitting the ground or something solid. Whiplash. I slipped on a wet floor and caught myself just before my face hit the floor. You guessed it. I got whiplash.
The action of the injury comes from the fact that your head and body are not connected solidly together. They are attached with a flexible string (the neck). Think of a rope between two cars. When the first car begins to move the second car, the rope in the middle stretches and, if the tug is too fast it can actually break. The stretch is on the ligaments that hold your neck bones together. They aren't designed to take that pressure. It only takes a microsecond to tear the ligaments before the muscles can tighten up.
Many studies done by research groups, insurance companies, car manufactures and others have shown that many factors are involved in how severe the injury can be. Body and head position, advanced warning, head turn at the time of impact, type of vehicle and weather conditions all are important factors. Accidents which happen at speeds as low as 5 to 8 mph are strong enough to cause considerable damage to the body. If both cars are moving or if the brakes are not tightly locked there is less damage to the car because it can move during the impact. Unfortunately, because the car moves more the forces on the body are greater and the injury is greater.
Once damage (even a little bit) has occurred the muscles will become protectively tight and develop TPs. Finding and treating TPs in the neck should include the muscles in the front as well as back of the neck. A simple way to do those in back are to lean way back in a chair, fold your fingers together and cup your hands behind your head as if you were daydreaming on a nice afternoon. While your head is falling back but being supported by your hands take one (only do one at a time) thumb and press the tip of it into the muscles along the neck from the bottom to the top just under the skull. If you find a TP maintain the pressure until it begins to feel a little better. It's tempting to try to get rid of the pain by applying more pressure for a longer time but it can actually make it worse. Don't do it.
For the parts of the muscles at the top and back of the shoulders try to find a large hooked tool like a curved cane handle. Hold the hook of the cane onto the top or back of the shoulder and pull with the hands so it applies pressure into the shoulder region of the neck muscles.