It is said that life is but a dream. Conversely, dreams are but part of life. The two are part of the greater whole. Each reflects the other as physical reality mirrors the non-physical.
Lucid dreams, while clearly owing a lot to the imagination, often contain a spiritual element which is not merely "imaginary."
Dreams have played an important role in almost all spiritual traditions. So what is this mystery that takes up large portions of our night, but about which we know so little?
Does insomnia cause depression? Does depression cause insomnia? Chronic insomnia is strongly associated with mood disorders, but which way does the causality run?