You misinterpret- any given hallucination or dream is merely based upon either personal or emotional experience. You have had no personal nor emotional experience with me. The mind is certainly unknowable, in that I agree- but I also know that it can only run so many variables at once. So to have any conversation that doesn't repeat itself, would require two people, thus I exist. If I were not to exist your theory In and of itself would be invalid because in the asking if me to prove I exist you have admitted in and of yourself, at least in small part that I do exist.