Just watched Inception and got a question.?

When the characters were in the van during the first level of the dream, the sharp turns affected the balance of the next level (the "hotel" dream world). People were rolling and falling about as that world shook and turned. Yet, when the characters were asleep in the hotel room during the shaking and turning of that hotel (which i would ume was tossing their bodies around) there was no affect in the next level down ( the"snow" dream world). Did I miss an explanation for why this is?