What are the minimum tests needed to diagnose carsickness?

Rding in a car: No special tests, it is a very individual thing motion sickness affects different folks differently, dramamine (dimenhydrinate) can help.

Accurate history: A careful interview (history) will help your provider determine whether you have carsickness (motion sickness). It is more common in people with migraines. Symptoms can have varying degrees of intensity. Typically nausea and feeling poorly occur when the car is in motion. The more winding the road, the more intense the symptoms. Looking out towards something on the distant horizon seems to help.