thats the thing, when he wakes up he gets some tidy bit of info stuck in his head, but he forgets a lot of his time spent there, like all dreams.
but if he did remember everything and shared it he'd be lauded as a lier/madman, i'm not sure how accepting this culture is at his era (probably very accepting, family treats the ghost sight like nothing) i guess a historian might do, but he better be good at finding and citing sources from the past to ever be relevant and not be laughed at.