If you haven't gotten motion sickness in other vehicles or RVs, then I agree that it might not have been motion sickness. What were your symptoms? Dizziness could be many other things - even something as simple as slight dehydration. Stomach could be something you ate as drsolo mentioned, and so on.
How long were you in the van? If you were only in it for 1/2 hour or so, then I can't imagine you'd have motion sickness so bad it lasted for hours afterwards. Unless you have an inner ear infection, etc., that's throwing off your equilibrium.