Actually, rather logical. I do have an explanation... or maybe multiple, depends upon your specific situation. It includes multiple unknowns to me, but something if you have time and the desire to consider. Consider where exactly you drove from and to exactly like the route you get the most queasy on, what you drove past, your personal sensativities/allergies, etc, if you get motion sickness to any degree... You don't need to write me or the board about this, this is just for your own personal interest, and fun for me to think on sciencewise. 5 possible explanations:

-The Cobb area is fairly close to multiple geothermal vents. Do you know if you drove past any? Some people have a sensitivity to sulfur and other particles found in the steam that vents.
-Since the 1960's the grape crop has dramatically increased in Lake County for the wineries in Sonoma and Napa. Plus the whole county is huge on Ag... Did you go past any specific farms? They do often us pesticides, toxins that affect the central nervous system. Yes, a wiff of something you are particularly sensitive to can cause dizziness, guiddiness, momentary disorder, etc... A little shouldn't do much but if you live(d) near one of the farms, you could be worried. It tends to build up in the system and stay, some of it.
-You also did cross multiple faults, the southeastern side of Lake County is riddled. Some people claim to be able to witch water (the stick someone holds and is supposedly able to find a slight shift in the magnetics of an area when crossing water or underground powerlines, etc.). I've seen it done my self for buried power and utility lines by a driller I worked with often... and Goodness sake it actually works. Kept us from hitting a gas line and telephone/tv cable before when there was no specific evidence I could find. Water is well known for flowing along fault lines, it looks for the easiest path and the fault has already broken through the earth for it. There is supposedly a slight variation in the magnetics around the flow/path of water. Every try witching??? You can find the placements of the fault lines at USGS and overlay the local roads with it to look at your route. If it happened at the same spot(s) everytime, you may consider what you are sensitive to.
- If it was a very windy road just prior to your queasiness, then you may simply be motion sick. Do you need stuff to get through a plane ride? Amusement park ride? Ever get sick on long very windy roads?
-a fifth explanation could be psychological... do you dislike mom-in-law? nuff said...