Answer: A vigorous, energetic state is called a day. When we are asleep, we exit from our prior state and connect with the next, active one. A dream is a small state (VaK – Vav Ktzavot), through which our prior, awakened state connects with the next active state.
It is similar to the neutral gear of a car transmission that is used in between the gears when we switch from first gear to second and then third gear. They are separated by a neutral gear, this is the dream at night.
If not for the neutral gear, we would not be able to switch from the first, to the second, and then to the third state. We cannot ascend to other states without sleep.
This explains why sleep is so important and why it takes so much time: 8 hours! When we are still in our egoistic nature, i.e., if our natural intentions are oriented towards our own sake, we just have to follow the demands of our physical needs. RAMBAM writes that a regular person must have enough sleep.
While we live in this material world, we must behave normally, and a night’s rest is a simple, physiological process that helps make this possible. If a person has already attained a spiritual level and acts for the sake of bestowal, then why does he need a night’s rest? What does it mean to us?
Dreams may be consequences of the events that we experience during the day. Our aspiration to attain higher spiritual states during the day allows us to make a spiritual ascent while we sleep, or to at least make relevant clarifications.
The wisdom of Kabbalah refers to the night’s sleep as a continuation of the day, a continued vigorous state. Sleep is physiologically essential, both for those who live only within the boundaries of this world and those who dwell in the upper world, at a spiritual level.
From KabTV’s “A New Life” 1/11/15