But motion sickness is when there's acceleration. That is, the physical acceleration is the cause of the sickness. It's not the visuals.
VR sickness is when there's somewhat equivalent visuals, but not acceleration. So I could see motion sickness and VR sickness being essentially opposites.
Arm-chair psycho-psychologist: Extra attuned to your eyes, and you get VR sickness because your body keeps refusing to follow what your eyes are telling your brain. Extra attuned to your body, and you get motion sickness because your eyes keep refusing to confirm what your body is telling you.
Anecdotal evidence: if you get motion sickness, you can help mitigate it by focusing on the horizon (ie, feed your eyes what your body is already telling you).
If you get VR sickness, maybe you can concentrate your focus on your body/breath to mitigate.
VR sickness is when there's somewhat equivalent visuals, but not acceleration. So I could see motion sickness and VR sickness being essentially opposites.