This might sound incredibly stupid but why do I get nauseous from playing specific video games for a long time? I can play rpg's for hours and feel just fine, but as soon as I start with Minecraft or even some first person shooters, I feel sick even after 10 minutes.
Games that I feel fine playing:
RPG's, racing, platform, some fps', puzzle/strategy
Games that make me sick:
Minecraft, some fps'
You might have some motion sensitivity involving head bobbing, which creates an ocean-sway movement effect (similar to actual walking) that can cause nausea in some people.
Minecraft does allow you to remove this bobbing (making the camera move smoothly) in the video settings, which will likely eliminate (or at least reduce) the nausea incurred. While I can't guarantee success, it's worth giving a try & if it does help, see about disabling it other troublesome games as well (if that option is available).