An abstraction of the concept of sleep. I love simple visuals that represent complex ideas and this is my take on sleep.

The outermost area, the lightest, represent our waking state.

The outer rectangles represent different stages of sleep, and the third rectangle is where dreams occur. Here, conscious awareness of the external environment disappears (this level is also referred to as paradoxical sleep because the sleeper, although exhibiting high-frequency brain waves similar to a waking state, is harder to arouse than at any other sleep stage. Vital signs indicate arousal and oxygen consumption by the brain is higher than when the sleeper is awake.

The darkest patch in the very centre draws the eye and all the visual attention. This section is not black, but a colour called Eigengrau, a deep shade of grey that we actually see in total darkness, as there is a certain level of signal noise that the brain perceives. This section represents deep sleep.