In the past, I have had rare, sporadic episodes of mild nausea as a passenger in cars. However, in the past month, I have experienced sudden and severe nausea when I am a passenger on long car trips. Twice, I have been a passenger on long car rides in the past month. On the first one, I become so nauseated that I vomited. On the second trip, I also became incredibly nauseated, leaning over a bag the whole time, but I did not vomit. Once I got out of the car, I still felt mildly nauseated for at least an hour or so afterwards. Any ideas as to what this might be? It is incredibly unpleasant.