Riding in a car makes me sick now!!!!
It is probably from your body dumping hormones and changing so fast paced. You can drop blood pressure and things very quickly now. Make sure you are well hydrated and see your doctor about motion sickness pills for the meanwhile. Also try not to eat alot in the car. If you had high cholesterol before surgery, you could actually be breaking off chunks of cholesterol into your inner ear. This is what I was told by the ear, nose and throat doctor when I had vertigo. It is a common cause of vertigo, which is dizziness, but could possible be a motion sickness trigger too? Worth asking about.
Wendy