It actually happen a lot with GTX680 and XIV thanks to crappy drivers. This has nothing to do with overheating. There is a thread about it on Nvidia forums.
And I can confirm this as a GTX680 owner.
Even if it is true that XIV generates a lot of heat, the 680 is way more efficient than its predecessor (I used to have a 580 before), and the fan doesn't even need to go above 50% while XIV is running (which keeps you a lot of margin before having your card to overheat, as the fan speed will be automatically increased as the temperature rise.)
It's easy to tell if overheating is the cause of an issue, just listen to the fan, at max speed, when using the default cooler of 580/680, it sounds like an airplane... Impossible not to notice. As long as the fan isn't at 100% it means that the temperature is below an acceptable threshold.
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To the OP, does it happen most of the time when you are in Ul'dah? If yes don't even look further, there is no way to fix this issue. Just wait for ARR.
(I also tried tons of different drivers, it happened with all of them, no exception, however I cannot tell for sure if it would happen less often with certain drivers.)