I figured it was more

  if (areEyesDetectingMotion != isBodyDetectingMotion) vomit()
If it was just eyes and ears it doesn't seem like VR motion sickness would be such a thing.

I don’t follow. Are you under the misapprehension that ears was referring to auditory perception, rather than vestibular sense of motion?

I suppose you could design an experiment that mucked with proprioception but not the vestibular system. Count me out as a test subject.