If you have zero symptoms, no dizziness, headaches, loss of consciousness, etc, relax. Because all they will do is run up $2000 in medical bills doing a pointless CT scan (after which they will either tell you 'you had a concussion' or 'you didn't have a concussion' and they'll send you home and tell you to take Tylenol). Just be observant and if any neurological symptoms arise (coordination, memory, headaches), then you might want to go get checked.

I've been through this a couple of times, both times I was cold cocked in bike crashes and evacuated to the ER by ambulance. That's a slightly different scenario, they CT scan you when that happens. The CT scan made my medical bills higher, but that was about it. A precaution. You know, one they didn't even have prior to 1980 or so (or whenever) and people used to whack their heads all the time.