There is a phrase used by the Mexihcas: ‘The person who doesn’t remember their dreams is one of the living dead, as they have no control over their life when they’re awake.’
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The main reasons to become a dreamer, according to tradition, are to deal with your past lives and the fragments of yourself that are imprisoned in the underworld, and to prepare yourself for your next death. A person who is able to dream consciously will die consciously.
Sergio Magana, The Toltec Secret: Dreaming Practices of the Ancient Mexicans
If we cannot remain present during sleep, if we lose ourselves every night, what chance do we have to be aware when death comes? If we enter our dreams and interact with the mind’s images as if they are real, we should not expect to be free in the state after death. Look to your experience in dreams to know how you will fare in death. Look to your experience of sleep to discover whether or not you are truly awake.
Tenzin Wangyal Rinpoche, Tibetan Yogas of Dream and Sleep