Lord Byron's "Darkness" is written in the "dream vision" form that is found in English poetry as far back as Chaucer, the first to write poetry in English, who wrote many dream vision poems, including The Book of the Duchess and Parliament of Fowles. A dream vision poem identifies itself as such from the very beginning. In Byron's poem "Darkness," Byron identifies the poem as dream vision from the first line: "I had a dream... ."
Lines 6 and 7 are two that confirm that the poem is a dream vision:
Morn came and went—and came, and brought no day,
And Morn came and went—and came, and brought no day,
The poem goes on to talk in a surreal, dream-like manner of desolation, selfish prayers for survival, forests on fire, famished animals and people, progressing through the entire vision to the loss of the moon and with it the tides as Byron comes to his surprise ending: "She was the universe."
The function of the dream vision, or dream poem, is to frame the extraordinary tale that the poet wants to tell. These were a standard form that Chaucer was introduced to on his diplomatic trips to Europe and have remained in English poetry throughout time, though much less popular now. In fact, it may be suggested that the framing technique used in dream visions inspired the frame story popular in novels and short stories.