25 years of our life is spent in sleep. The Tibetan culture views our dream life with equal importance as it does our waking life. Tenzin Wangyal Rinpoche has written a lovely and accessible book on how we can learn how spend that time in active and deep meditation.
http://www.amazon.com/Tibetan-Yogas-Dream-Sleep/dp/1559391014/ref=sr_1_2?s=books&ie=UTF8&qid=1306340677&sr=1-2
