Well, some dizzy is to be expected, after a knock to the head. However, I did end up checking in. They pushed me through in less than an hour (after much laughing about forcing the still-on-duty security officer into a hospital gown for x-rays), which is an incredible record for an ER.

Diagnosis? Whiplash. They said the headache is normal at this point, but if it's not gone by tonight when I come in to work they're running me through CT, just to be safe.