Flow My Tears, the Policeman Said

Flow My Tears, the Policeman Said is a paranoid science fiction novel by Philip K. Dick.

Scrutinizing him, she said, 'Maybe your're not a celebrity; maybe I've reverted back to my delusional period. They said I probably would, sometime. Sooner or later. Maybe it's later now.'
'That,' he pointed out, 'would make me a hallucination of yours. Try harder; I don't feel completely real.'
She laughed.