If you play the VR with your elbows not still then your adding in another xzy axis for your mind to calculate as it moves your elbows and arms.
But if you keep your elbows on a surface to keep them still as you play vr this xyz axis isn't being calculated because your elbows aren't moving in the xyz axis.
So if you get nauseous, try to keep your elbows on a flat surface, your feet and elbows still and then the brain isn't calculating the xyz axis of the feet or elbows and so it just calculates the vr xyz.
I think the brain calculating for the elbows and feet xyz as they move is causing brain strain and over calculation and this leads to nausea.
When people make vr controllers like the 1 oculus showed at e3 they all focus on the hands, not the elbows. That's exactly wrong, if my theory proves true by a nausea tester of my theory says it's true.
Well, the Vive and the Morpheus demos actually feature no elbows. In the case of the Vive, you only see the controllers themselves and in the Morpheus (London heist demo) you only see your hands (in gloves), but nothing below your palms. That seems to be a smart decision to me.