This happened to me briefly yesterday, I was in the first town in Dushaan. I was standing next to a quest NPC, outside, and I simply jumped up. Then suddenly the entire world disappeared(including my character) and all I saw was sky all around. I waited a good 15 seconds before I exited and reloaded, and then it was fine.
Latest Drivers/Updates all around.
I would try doing a /stuck and see if that helps.