The mysterious significance of sleep has yet to be realized by the Western thinkers as it has been by those of the East. It is an independent and distinctive aspect of life with special characteristics too important to be undervalued and too decisive to be ignored. Our great error has been to neglect its investigation, to relegate it among the curiosities of nature when we should have vigorously pursued its ultimate meaning. The secret of life cannot be got from the study of one side of it only--the waking. Man's research must embrace its obverse side too--the sleeping.
-- Notebooks Category 19: The Reign of Relativity > Chapter 3: The States of Consciousness > # 27