Within the act of falling asleep, the brain (actually neural activity) goes through remarkable transformations. Paintings and sculptures I have done in the past depict the geometric, fractal and architectural shapes neural activity forms by the thought process. As one falls asleep the concrete form of neural activity, morphs into a liquid state, which resembles the dynamics of ink droplets in water (see animation below). Like matter there are three different states to neural activity, solid, liquid and gas, and the transition states are the same. As the active thought state of rapidly changing stark geometry , looses form as you fall asleep and becomes liquid, with typical fluid dynamics that change geometry to flow. As one falls deeper into sleep (but not REM sleep) the transition to gas is made, where fluid form of decreasing thought becomes more dispersed and less capable of concrete thought into the gaseous form. In this state it is not simply the brain activity that falls off, but as depicted in the sleepers head here, you loose your worldly mass, and even your flesh starts to fall from your awareness. As you fall deeper into sleep and the solidity and weight of your body dissipate into the ether, your neurons also take a rest and alow you to become something akin to air. In my version of sleep your thoughts and body dissipate and transition towards the gaseous. The act of falling asleep is similar to becoming a cumulus cloud, drifting and morhing with the air currents.