He probably started out by having minor hallucinations and delusions. After that, he probably became paranoid, and then he went insane.
John Nash had paranoid schizophrenia, which included delusions of persecution (thinking that people were "after" him) and disordered thought.
According to the autobiography of John F. Nash Jr. on the Nobelprize.org website: "The mental disturbances originated in the early months of 1959". Please see the related link.
he isn't dead
Yes Steve Nash is related to Rick Nash