The receiver and his occult source
Occult books contain knowledge about the occult, black arts, witchcraft, rituals and how to communicating with spirits and demons
According to what we know about Nostradamus, he seemed to have possessed a number of old books with occult knowledge. It looks like these books included information about how to treat metals. Treating metals generally falls under chemistry, requiring chemicals. You might therefore presume that the author of such a book might have had knowledge about alchemy / chemistry.
From the letter to his son we learn, that when Nostradamus finally destroyed his books they burnt with a strange bright light. Were the pages of the books maybe impregnated with some kind of chemical that produces intense flames when burnt? If that is true then consuming such substance (by touching the leaves of the book and then your mouth) could have caused any type of sensations. Including it could have aided in getting into a trance or getting hallucinations.
Receiving visions from an occult source suggest a passive roll with no interactive communication. In the case of Nostradamus this is not certain. It is said that Nostradamus predicted his own death and the year that people would open his coffin. These events can hardly be called main events of history. If Nostradamus was relying entirely on the occult source, than this entity must have given him also information about events relating to his personal life. In that case the source must have known who he was. That sounds a bit freighting, but is a very interesting idea that the occult source not only gave information about main events in a far future but as well about (almost current) events relating to the seer himself.
The receiver is the individual that receives, more or less interprets the message and records it.
As written under motivation, it is the intention of the receiver that strongly influences the final documentation of the vision. For instance if the prophet is religious than any visions received will probably be interpreted under that light and likely be given a religious meaning.
It is likely that a prophet chooses to be a prophet. He might wish to receive prophecy and participate in the rites that are necessary to do so. However it seems to be the sender that has the final word and select prophets. However, nothing is known how the sender knows about the receiver and how he can be sure selecting the right ones.
It seems that prophets play a far more passive roll than we thought they had.
In our world prophets receive visions and write documents. We know and respect them for their work. But in the overall picture the roll of a prophet might be rather small.
First the prophet is not in control, he does not choose the sender - he gets selected. The prophet does not know who the sender is. The sender might introduce himself any way he wants and it is up to the receiver to believe him and to form some kind of idea. It is the sender that initiates and terminates the communication. If there is any advanced technology involved than the prophet is not aware of this.