Augustine of Hippo, On Care to Be Had for the Dead Chapter 14

14. Like dreams, moreover, are also some visions of persons awake, who have had their senses troubled, such as phrenetic persons, or those who are mad in any way: for they too talk to themselves just as though they were speaking to people verily present, and as well with absent as with present, whose images they perceive, whether persons living or dead. But just as they which live, are unconscious that they are seen of them and talk with them; for indeed they are not really themselves present, or themselves make speeches, but through troubled senses, these persons are wrought upon by such-like imaginary visions; just so they also who have departed this life, to persons thus affected appear as present, while they be absent, and whether any man sees them in regard of their image, are themselves utterly unconscious.