Smelling Cigarette Smoke (Phantosmia): What could it mean?

At some point in the past week or two I started smelling cigarette smoke where there definitely was none. Initially it was just a brief whiff while sitting in my easy chair and then it would be gone, but now I smell it everywhere. And it's no longer just a brief whiff - it's almost constant and to the point where it sometimes makes me feel nauseous.

I have recently increased the amount of Gabapentin I'm taking from 300 mg/day to 500 mg/day. Is it possible the increase in Gabapentin has anything to do with this?