The picture above* is of the Glymphatic System and it awakens when we are asleep. On the left is a picture of the system during a sleep cycle. The red area is the CSF flowing through the brain. The CSF was no longer contained just in the ventricles, but flowed through the brain. And it happened much less when we are awake. And there was a direction of flow. In brain tissue, the direction of flow is from a high pressure system to a low pressure system. From an artery to a vein. The CSF flows through the brain picking up waste, cleaning out debris, which happens when you are asleep.
This shows a dynamic change in the anatomy of the brain tissue during sleep. So essentially when you are sleeping, there is an increased flow of CSF through the brain tissue itself. Remember, the extracellular matrix, the interstitial network, it is essentially all one liquid matrix. Now it goes into the brain itself removing toxins and waste, byproducts that built up throughout the day of your living. This is natural. It is a waste clearance system. When you are asleep, these pathways open up in the brain tissue allowing the CSF to flow and clear out toxins, bringing in new replenished fluid. It is a powerful method of detoxification and why we feel rested after sleep. The question here is does this only happen during sleep? The presumption would be no. I hypothesize that it happens during deep states of meditation. Because sleep is a parasympathetic state, it could happen when in a profound parasympathetic state in meditation. You can activate your Glymphatic System in mediation, or in a state of rest and repair such as deep body work.
*Study published 2013, Science Magazine Oct. 18; Sleep Drives Metabolite Clearance from the Adult Brain: Lulu Xie1, Hongyi Kang, Qiwu Xu, Michael J. Chen, Yonghong Liao, Meenakshisundaram Thiyagarajan, John O’Donnell, Daniel J. Christensen, Charles Nicholson, Jeffrey J. Iliff, Takahiro Takano, Rashid Deane, Maiken Nedergaard: http://science.sciencemag.org/content/342/6156/373