The Great Dark, Mark Twain — (unfinished, published in 1962 as part of the formerly suppressed, Letters from the Earth) “A pleasant bourgeois chap peers through the microscope he has just bought for his daughter into a drop of water and is astounded by the monsters he sees…” He falls asleep and dreams of a life in the compressed world of the drop; while adventuring there, he believes his past life was a dream. Upon waking, although he’d slept only for a moment, he now believes that his waking life is a dream.
Comments: Online text at Project Gutenberg. See H. Bruce Franklin’s commentary in Future Perfect: American Science Fiction of the Nineteenth Century, which compares the piece to Connecticut Yankee. “Twain’s ambition was nothing less than to express the relations between dream and what we call waking reality as the reversible relations between a nightmare microcosm of infinitely expanded time, in which the most incredible horrors become humdrum, and a waking cosmos of infinitely compressed time, terrifying because of what its humdrum activities hide.” (Franklin)
Author: Wikipedia: “Samuel Langhorne Clemens (November 30, 1835 – April 21, 1910), better known by his pen name Mark Twain, was an American author and humorist.”