Hmm... that is interesting. The first thing I thought of would be some kind of physical brain problem- if the sinus infection thing doesn't work out, seeing a neurologist would be a good bet. However, it could be a myriad of mental disorders as well, hopefully something not too serious like anxiety. Either way, I'd start with a neurologist and rule out anything physical.
In the mean time, it sounds kind of like the derealization that comes with anxiety disorders, and that could explain the nausea too... but I'm not really sure about that.