Complex sentence: Shortly afterwards Johnson caught a cold which turned into bronchitis, lasting for several months, and his health was further complicated by "feeling forlorn and lonely" by Levet's death being accompanied by the deaths of Johnson's friend Thomas Lawrence and his housekeeper Williams.
Split into simpler sentences: Shortly afterwards Johnson caught a cold which turned into bronchitis, which lasted for several months. His health was further complicated by "feeling forlorn and lonely" over Levet's death, and by the deaths of his friend Thomas Lawrence and his housekeeper Williams.