This is the only book I have ever wanted to read twice, and as far as I can rememeber the only one I have read twice. Through intellectual analysis (rather than new-age bs) it changed my view of consciousness.

It begins with a survey of historical sources of sleep (Upanisads, Gita, commentaries altering explanations of deep sleep to finish with modern interpretations of the state from the very active field of current Indian philosophy. The overall theme of this book is a critique/explanation of why sleep can be used as an (imperfect) model for Brahman-experience. This book is full of Sanskrit terms as well as english philosophical terms and is not for the casual reader, but for those with serious interest in philosophy, consciousness, and/or advaita vedanta, it is an essential read. Any serious and enthusiastic student of this subject will be able to extract many layers of understanding of reality from this well-organized text.