Barfogenesis
That seasick feeling some people get with virtual reality headsets. Caused by a conflict in the brain: the eyes register movement, but the inner ear doesn't feel it.

The first step to success, says Linden Rhoads of Virtual i-O, "is moving away from a helmet paradigm to a glasses paradigm." Glasses are lighter than helmets, and that helps reduce motion sickness — too much weight can throw off the brain's sense of how to move. In the trade they call it "barfogenesis."