I doubt you had anywhere near the forces required for a whiplash injury. You did not get the whip of whiplash when you bumped your head. Theoretically, this could have aggravated your previous whiplash injury but your tightness could also be nervous/anxiety tension. Maybe you need a good massage to help you relax.

60 G's is the usual minimum for a concussion but many tolerate up to 80 to 100 Gs. The brain can tolerate even more Gs for shorter periods of time. A punch has follow through so the impact covers a longer period. A bump into a stationary object does not so the later has a very short time span.

Take an OTC pain med and relax. You will do better when you can let go of your anxiety and tension.