ETA: I called the doctor's office asking to talk to a nurse, figuring they'd tell me it was probably an ear thing and to wait and see what happened. But no, if I think it's worth calling the doctor, they always think it's worth getting me into urgent care.
Hopefully this one won't then lead to the ER.
ETAYA: Labyrinthitis. A prescription for corticosteroids and a recommendation to try motion sickness meds. I figured out that chewing gum helped on my own. Doc says 3-5 days is likely, and to call if it lasts longer or gets worse or changes.