Odd you should mention that. The one time I was fairly certain that my recently deceased father was "present" in my home, one of the reasons was the unusual smell of his tobacco (he was a pipe smoker). It was not smell I had ever smelled anywhere else, but it was sharply present in my room that morning.

As far as a remindment of odors past, they are not hallucinatory. Some studies claim that olfactory is one of the most vivid links to past moments, and faint traces of a smell can suddenly present long-buried memories of timmes and places long past.

A