In my childhood, I read a short story about a man who lands on Mars and finds that Martians looked exactly like humans. When he told them he was from Earth, everyone thought he had a disease that makes him hallucinate. So he takes some Martians to see his space ship, and they think they caught that disease from him. He's later sent to a hospital/asylum where he meets martians who really had that disease. Unfortunately, I don't remember how it ended.
It seems to be the story The Earth Men, part of the Martian Chronicles bundle of short stories by Ray Bradbury. From Wikipedia:
This story tells of the "Second Expedition" to Mars. The expedition is a group of 4 men. The astronauts arrive to find the Martians to be strangely unresponsive to their presence. The one exception to this is a group of Martians in a building who greet them with a parade. Several of the Martians in the building claim to be from Earth or from other planets of the solar system, and the captain slowly realizes that the Martian gift for telepathy allows others to view the hallucinations of the insane, and that they have been placed in an insane asylum. The Martians they have encountered all believed that their unusual appearance was a projected hallucination. Because the "hallucinations" are so detailed and the captain refuses to admit he is not from Earth, Mr. Xxx, a psychiatrist, declares him incurable and kills him. When the "imaginary" crew does not disappear as well, Mr. Xxx shoots and kills them too. Finally, as the "imaginary" rocket remains in existence, Mr. Xxx concludes that he too must be crazy and shoots himself. The ship of the Second Expedition is sold as scrap at a junkyard.