I was involved in a rear end collision in 1993. That day there was very real pain in my lower back and my knee (which hit the steering wheel). It was 2 days later when I really started feeling the pain in my neck and numbness and "electric shock" type pain that radiated to other parts of my body.
The real indicator of serious nerve or spinal cord damage is numbness in any part of the body or "electric shock" type of pain. If numbness or "electric shock" pain radiates from your neck or back to other parts of your body, watch out.
I ended up having a discotomy (sp.) where the disk between c5 and c6 (cervical vertebra #5 & #6) was removed and bone tissue from my pelvis was inserted. Essentially a bone graft. These 2 vertebra are essentially one bone now, there is no flexibility there anymore. The disk was to damaged to repair and disk tissue does not heal itself. It can be manipulated to reduce swelling/herniation, but it does not repair itself like other tissue can.
I would consult your doctor if you have medical insurance, if you do not you might want to contact his insurance company and ask them about being checked out. You should get checked out regardless, better safe than sorry.
Meanwhile, plenty of rest, LOT'S of water, an Ibuprofin type pain reliever (something that's an anti-inflammitory type drug)if necessary.
Good luck.