I'm sore from a car accident?!

Your back muscles tightened up to give you the knots there and to get rid of them you have to free up your back muscles and here's how to do that:
Back:
(do from a sitting position)
Place your left hand on your left leg next to your body. Place your right hand over your left shoulder, fingers over the back and the palm in the front and firmly pull down on them and hold. After 30 seconds slowly lower your body forward and to the outside of your left leg, keeping your left arm fairly straight as you do. When you reach your lap remain there for another 10 seconds, release the pressure but rest there for another 30 seconds. Then reverse your hand positions and do your right side.
For best results relax your body first by taking a deep breath and exhaling then remain this relaxed.

I would definitely go to a hospital and get checked out. Chances are last night you didn't feel much of anything because you were in shock; therefore didn't feel pain. Your injuries could still be soft tissue injuries, but why take the chance? This is your life you are talking about - don't fool around with it.

Life; and the rocks it throws at you

Of course.

my head