Friend of mine got rear-ended like that a few years back, pain didn't start really kicking in until a few days afterwards, she still has problems from the accident. Take it easy for awhile, and if the pain doesn't get better or subside get it checked again.
Her car was a hair away from being declared a total, from all appearances it should have been, but was fixed instead. She got rid of it a short time after, it never drove the same.