"I used to suffer from schizophrenia, and now we have recovered." What does this joke mean?

In fact, he still thinks he is two people.

Just like another joke, a mental patient thought he was grass and was finally cured. On the day of discharge, he met a mental patient who had just been admitted to the hospital and wanted to shake hands with him. He said "hello, I'm a sheep ~", which scared the man away. The doctor caught up with him and said, don't you know that you are not a grass, but a person? As a result, he said, "I know I'm not a grass, and he doesn't know!" "