I had sinus surgery several years ago. My ENT told me that my nasal airways were the equivalent of cocktail straws. After surgery I couldn't smell anything for a short period of time and then the Phantosmia started. There was one day in particular where all I could smell was rotting trash. I cleaned my house from top to bottom believing that somewhere there was a piece of rotting food. I even had my sister come over to help me find the culprit. She couldn't smell anything foul. She said that my house smelled nice and clean. The Phantosmia lasted for several weeks and it would come and go. After I healed and was fully recovered from my surgery all episodes of my olfactory hallucinations ceased. It took me a while to trust my sense of smell after that. If I was around a bad odor I would question if it was really there and would have to ask someone else if they smelled the same thing. You don't realize how much your sense of smell means to you until it is compromised.
Watch the video below to hear the story of a woman with Parosmia.