Weird, my brother went through this exact thing. So around Thanksgiving time he felt dizzy while driving on the freeway so he pulled over and we went to pick him up. Then he was fine but experienced it again about 2 weeks later. He went to the doctor 3 times and they said it was just vertigo/motion sickness. The doctor said that his blood pressure and all that were fine so it was nothing major. He even had a blood test done and they didn't find anything noteworthy (4th trip to doctor just to learn the results :P).
The Doc also said it might just be a bacteria infection affecting his balance. For the first month or so he was still experiencing vertigo while at work. He's not been driving since then in fear of crashing so we've been taking him to work and back. I personally think it's all psychological. Sometimes when you worry about something or just do too much of something your body becomes imbalanced. It's like now he's afraid of driving because of what happened. However, I put my foot down when he asked me to take him to work last week so it forced him to drive. He's been okay so far so hopefully he will get over it.
I still don't know exactly if it's just vertigo/motion sickness or something else but it's been about 3 months. He might have been over it already but was just afraid to drive, who knows. I mean so far he hasn't felt dizzy or anything like that. I'm still curious about it though so let me know if you find something out from your doctors.