Complex sentence: In September 1949 Formby went on a 19 city coast-to-coast Canadian tour; he returned unwell and, while appearing in "Cinderella" in Leeds, he collapsed in his dressing room.
Split into simpler sentences: In September 1949 Formby went on a 19 city coast-to-coast Canadian tour, from which he returned unwell. While subsequently appearing in "Cinderella" in Leeds, he collapsed in his dressing room.