Since it is impossible to dream something you've never seen, we can lay to rest the claim that those who have seen visions of things they've never before seen are just dreaming.
Wrong.
Those with "visions" or visionary dreams just combine a patchwork of things they have aready seen and their brains have stored somehow.
If you dream of a Rhino you MUST have seen a Rhino at least once in your life, but maybe you cannot remember that, when awake..
It has to be very clear that, paticularly in todays media flooded world, almost every human beeing has seen phantastillions of images when he is a child of 10. He will possibly not remember that he was in horrible fear on a boat while it was a little windy at the age of three, but his brain will have this information stored in some pretty unused neuronal connections.
And then this person sees a ship, his brain suddenly unzips that file (because the ways of the brain are mysterious) and he get an adrenalin rush seein raging waves, sea monsters, death and destrucion.
Boom, there is a vision.
As chance would have it, ths ship sinks. And voila, we have a new story for the boulevard.