"as Coleridge once discovered"

Samuel Taylor Coleridge (1772-1834), the Romantic poet, was a heavy user of opium throughout almost all his life.  In his own account of the origin of his famous poem Kubla Khan, he implies the inspiration for the work came from a particularly vivid opium dream:

The author continued for about 3 hours in a profound sleep, at least of the external senses, during which time he has the most vivid confidence, that he could not have composed less than from two or three hundred lines.

A recording of a reading of Kubla Khan can be found here.