How can "Kubla Khan" be considered a dream poem?
Samuel Taylor Coleridge's "Kubla Khan" is often thought to be a dream poem, and for good reason. A short, descriptive line before the beginning of the poem describes it as "a vision in a dream," while Coleridge himself claimed to have "composed" the poem in response to a vision he had while sleeping. Thus, it is reasonable to suppose that the poem is either meant to describe a dream sequence or, at the very least, a fantastical dream world.
Furthermore, the imagery within the poem suggests a magical dreamscape. For example, Coleridge describes "A stately pleasure-dome" (2), "gardens bright.../ Where blossomed many an incense-bearing tree" (9), "Ancestral voices prophesying war" (30), and "A damsel with a dulcimer/ In a vision" (37-8). All in all, the poem takes us on a tour of various fantastical images, many of which seem to spring to life spontaneously and without prior explanation, just like images in a dream. As such, given the fragmented, exotic, and almost magical nature of the poem, it would be perfectly plausible to assume that Coleridge is, at least in part, describing a dream sequence.