By Dr. Mercola
Healthy sleep consists of several stages, and you cycle through these stages four to five times during the nightly sleep cycle. As a result, you’re progressively descending into deep sleep and ascending toward lighter states of sleep several times, and this cycling is tremendously important, both from a biological and psychological perspective.
During stages 1 and 2, your brain remains active as it begins the editing process where decisions are made about which memories to store and which to discard. During stages 3 and 4, you enter into a deeper, almost coma-like state, during which the actual physiological cleansing and detoxification processes in the brain1 take place.
Your brain cells actually shrink by about 60 percent during this deep sleep phase. This creates more space in-between the cells, giving your cerebrospinal fluid more space to flush out the debris. Lastly, in stage 5, you enter rapid eye movement (REM) sleep, where dreaming takes place.
All of these stages are important, and it’s important to cycle through them enough times each night — especially the deeper stages, and the longest and deepest REM cycle typically begins around six hours after falling asleep. If you only sleep five or six hours, you completely miss this important stage, and when deep sleep stages are missed, your brain gets clogged with debris associated with Alzheimer’s disease. You also forgo the psychological benefits of dreaming.
Why Dream?
Even if you accept the idea that sleep is important, you might not consider dreaming to be very high on your list of biological imperatives. Alas, you would be wrong. Dreaming actually serves a number of important functions. (Later I’ll also address the potential benefits of…