Complex sentence: Suffering from some stress-induced psychological disorders, including insomnia, in September 1900 he returned to Poltava where he experienced a bout of creativity and, having finished his Siberian short story cycle, published his third volume of "Sketches and Stories" in 1903.
Split into simpler sentences: Suffering from some stress-induced psychological disorders, including insomnia, in September 1900 he returned to Poltava. There he experienced a bout of creativity and, having finished his Siberian short story cycle, published his third volume of "Sketches and Stories" in 1903.