Diving Bells

Why is the film 'Diving Bell and the Butterfly' called?
I know it is a translation of the French title, but I am interested to know why it's called that
This is the book's prologue, the film is based. The direct quotation is … "My diving bell becomes less oppressive, and my mind like a butterfly in flight. There is much to do. You can wander in space or time, set out for Tierra del Fuego or court King Midas. "
THE DIVING BELL AND THE BUTTERFLY STAR TRANSFORMS