I assume the prescient information could be hallucination too.
Yes, there's two situations that I can think of where hallucinations would seem like presentience.
The first is that the insane person hallucinates another person's words in their mind and then hallucinates the other person's words from their lips. In other words, the insane person first thinks that they received a message telepathically and then hallucinate the actual words.
The second is that the person first hears actual words come from another person's mouth and then the insane person's brain creates a time lapsed memory of those words and places the created memory before the real memory, thus making it seem to the insane person as though they heard the words in their mind first and then the person spoke it whereas in reality the opposite happened.
I'm not aware of the limits of hallucinations, so it seems reasonable that just about anything could be fabricated.
How do you know that any of the words you hear in your day to day life are not hallucinated? How do you know that any of the metaphysical experiences you've had aren't just hallucinated? Hallucinations can indeed take on any form, so if we were to take this question to its philosophical limits then we would find ourselves in the "brain in a jar" or "Descartes' demon" scenarios, even for perfectly sane people.
So rather than assuming
either insanity or sanity, one should attempt to gather information and try to determine
which is more likely (while also noting the possibility that it could be a mix of the two) given how the information plays with external reality, and using a certain criterion for "is it meaningfully useful?". For instance, if I developed telepathy only to the point where I could hear someone else's thoughts literally one second before they spoke them, and that was the full extent of my telepathic ability, then it would be "meaningfully useless" in that I could not use it to any substantial gain. In the same sense, if an insane person is hallucinating voices then they would be unable to meaningfully
use that information. So in that regard, there's little distinction between real metaphysical ability and mere hallucination.
The important difference is that metaphysical ability can be developed in such a way as to be both verifiable and used to the benefit of the practitioner. Hallucinations, on the other hand, will never produce verifiable results and will rarely (if ever) benefit the person hallucinating; though if I'm wrong and a person CAN figure out a way to use their hallucinations to their benefit, then hooray for them because they're doing just as well as if they developed real metaphysical ability and used it for their benefit. If a person is so far gone into hallucinations that they cannot meaningfully distinguish between hallucinating metaphysical ability versus developing real metaphysical abilities, to the point where their brain provides false information so that it can pretend like it is performing metaphysics and/or so that it can pretend like it is benefiting the "practitioner", then all of this discussion is pretty much moot anyways.
EDIT: Oh, and one other meaningful difference between metaphysical ability and hallucinations is that you have to spend time developing metaphysical abilities, whereas people generally just kind of slowly fall further and further into dementia without having to do
anything and in fact would have to do
something in order to fight off the effects of dementia. Taking into account spontaneous enlightenment (or spontaneous advancement) that sometimes occurs, if a person does not put in effort over time
and yet supposedly continually develops over time
and yet is unable to put their "abilities" to meaningful use, then it can generally be easily determined to be hallucination rather than metaphysical development.
In attempting's case for this thread, as an example: he went through a spontaneous experience that is somewhat difficult to distinguish between real metaphysical advancement versus mere hallucination (because different portions of the description that he gave of the event allow for both possibilities), but time will likely tell the difference quite well.