Yeah, gravyyy, I've smelled a smell that did not exist. It was rotten chicken(!) (of all things!) It happened most recently a few months ago. That was the only time since I'd been diagnosed (BP II). It was the middle of the night and all of a sudden the thought of "olfactory hallucination" came to mind, and I can tell you I freaked out a bit, worrying it might be a psychotic indication. One time? No. It suddenly came rushing back that this has happened quite a few times (same smell). Boy, did I rush to the computer to try to disuade myself from worry. Nothing I read helped clarify one way or the other. I was freaking for the same reason as you. I felt clearly in touch with reality, so wth was this?! Upon thinking some more, I realized that each time it had happened, it was upon waking (usually in the middle of the night). I have had a considerable number of hypnopompic hallucinations (common, not psychotic, but *very* real!) and consoled myself that it was probably the same sort of thing (I don't know for sure, but it seems reasonable...)
(Interesting about the headaches, northern... I have migraines, but the smell thing has never been a precursor, though visual disturbances have, ranging from auras around lights to intense, strobe-like flashing at the edge of vision.)