Related, there is the possibility that posture during sleep may impact the efficiency of the glymphatic system
Paper: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4524974/
Press release: http://sb.cc.stonybrook.edu/news/general/150804sleeping.php
Paper: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4524974/
Press release: http://sb.cc.stonybrook.edu/news/general/150804sleeping.php
There's no human data at this point.
In the context of quack and alternative medicine the term "toxin" is used to refer to any substance supposed to cause ill health.
What the body produces and might need to eliminate is metabolic byproduct or waste, nothing to do with "toxins". The term used in this context makes me cringe.