I have found lots on info online regarding this phenomena. It's quite distressing, I've been smelling cigarette smoke for a about a week now. I'm under quite a bit of stress with family healthy issues, so I'm thinking it does have to do with stress. It's pretty awful. There are some good articles on Phantosmia, it's official name.It can be caused by some serious health issues, but at least I know others have it, I'm not going crazy. I even thought it could be a 'memory' from childhood, as my father smoked. I hate the smell the smoke, can't stand it, and the older I get, the more it bothers me. Also look up phantosmis and Leopold, and doctor who specializes in helping people with it. Thank you.