For some it's all in your mind. I have somatic delusions.
I'm not saying its always all in your mind. For some it is a real condition that you suffer with. But for a small percentage it could be all in your mind.
I lived for 7 years believing I smelled horribly of feces. I just knew it. I wouldn't bother to be close to people out of fear that they would smell me and react. I always looked for reactions. Everywhere I went it was always on my mind. When someone breathed funny, coughed, cleared their throat, or looked at me I thought they were doing it because I smelled.
I asked everyone if I smelled and everyone said I didn't. I was diagnosed as having psychosis but I didn't believe it. I always came to the boards to find out if I had gotten reactions and what reactions to look out for. I always read about the stories of people getting humiliated and thought that was what was going to happen to me.
They put me on medication and I started going out. People weren't doing what they did to the people on the board. They would stand close to me in lines and sit next to me in waiting rooms. They didn't cough or cover their noses when I was around and were really friendly to me. But I still believed I could smell. It took months for me to figure out I didn't. I was on the medicine 7 months before it dawned on me I didn't smell. It was like a whole new world opened up for me. I went out everywhere. And did things I never thought I could do.
I said all of that to say sometimes it is all in your mind. Even when you don't think it is. If no one has ever said you smell, and you only go by little reactions like someone coughing or sneezing it could all be in your head.