"Le Horla" by Guy de Maupassant is a horror story written in 1887. The tale follows a well-to-do narrator who begins experiencing disturbing physical and psychological symptoms after greeting a passing Brazilian ship. Through diary entries, he describes his torment by an invisible presence he calls "the Horla." As inexplicable events multiply, he struggles to determine whether this entity is real or a manifestation of his own descending madness, while his condition progressively deteriorates through paranoia, hallucinations, and anxiety.
Wikipedia page about this book: en.wikipedia.org/wiki/The_Horla Wikipedia page about this book: es.wikipedia.org/wiki/El_Horla