I'm not so sure of that. John von Neumann was approximately as intelligent as a human can be, and his mental health was good as far as I know.
However it has been reported, that he really did not handle the realization that he was going to die very well.
How exactly that handling manifested I have been unable to find.
He was a brilliant man and he was understandably terrified of the very mortal fate that awaits all of us.