This just demonstrates the importance of going to get checked out. I'm not so sure it's the case here, but many people choose to "sign off" or refuse treatment after MVA's, only to realize they have neck, back, or head injuries days or even weeks later. If you get into a car accident that is anything more than a fender bender, you really should go get checked out immediately, not matter how good you feel. You very well may not feel anything at the scene because your adrenaline is pumping so much from the accident, but you could easily have internal bleeding or a multitude of other problems and not catch the symptoms of it until it's too late.
Sure the hospital is a pain in the butt and nobody likes going, but it's better than going home, going to bed, and waking up in severe pain, or just plain not waking up at all. Think twice before you sign off after an accident.