What aspects of Gothic literature appear in “Confessions of an English Opium Eater” by Thomas De Quincey? How are these aspects significant to Gothic Literature themes?

"Confessions of an English Opium Eater" is an autobiography, rather than a piece of Gothic fiction, but it certainly contains several aspects that might be more at home in a Gothic novel. De Quincey's lush prose was much criticized as a paean to the very drug he supposedly sought to warn readers away from, and his languid, unfortunate narrator—his fictionalized self—could certainly be compared to the archetypal brooding Gothic hero.
Specifically, Gothic elements in this work include:
1. The landscape as a character. London, in this work, is described lavishly, and presented as somewhere mysterious, dark, and concealing hidden depths where anything can happen. De Quincey's descriptions of London at night foreshadow the urban Gothic of Stephenson and Wilde.
The idea of the hinterland, or borderlands, as part of a landscape is key to Gothic literature. It suggests a blurring of the lines, a place where all things are possible, and creates an aura of mystery. In this work, Oxford Street becomes a "stony-hearted stepmother," a symbol of the underworld in which iniquity thrives. The narrator presents it almost always as it was at night, with the cover of darkness, once again echoing Gothic tropes.
2. The Gothic archetype of the "doomed" woman, cloaked in shadow, almost a ghost as she lives—look at the descriptions of the narrator's "benefactress" in Oxford Street, "one of that unhappy class who subsist upon the wages of prostitution." This woman lives in the shadows, is the narrator's "partner in wretchedness," and yet is presented with a Gothic preoccupation that focuses on the fall of the innocent. A prostitute, she is nevertheless "noble-minded Ann," full of "bounty and compassion" and yet brought low by some sinister element.
3. A fixation on dreams, and the symbolism of dreams. The idea of being "haunted" appears again and again in this work: the narrator refers to his past misdeeds as having "tyrannised over my dreams" and "haunted my sleep." Elsewhere, however, dreams approach the Gothic ideal of the sublime, driven by the power of "mighty opium," which "to the guilty man for one night givest back the hopes of his youth," providing an "oblivion" in which the beauty of a man's thought approaches "Paradise." The Sublime is made possible through the ecstasies of opium, which produce "more than earthly splendour" in the narrator's dreams, but at the same time, "deep-seated anxiety and gloomy melancholy" overcome him. Gothic literature developed hand in hand with advances in psychology, and we often see an interest in what happens in dreams and how this is connected to the events of waking life and the affect of the dreaming character. This work explores this idea in depth, and inspired many others to pursue psychological storylines in their Gothic work.