The use of hypnotism can be traced all the way back to the time of the ancient Egyptian pharoahs. The Egyptians built marvellous "dream temples", which were watched over by one of their many gods. A person would travel to the temple, bringing with them an offering for the god. The priest would instruct them to lie down, then lead them into a trance and instruct them to dream an answer to the problem or question they had in their mind.
A person cannot be hypnotised against their will; they have to want to enter a trance. Given the amount ancient Egyptians invested in their visits to the dream temple and in their offerings to the gods, and the often long journey to reach the temple, they would be very willing to be led into trance and obtain a prophetic dream.