The glymphatic system (or glymphatic clearance pathway) is a functional waste clearance pathway for the mammalian central nervous system. The fact that the glymphatic system even exists is a recent finding, and one I did not learn in medical school.

However, we have come to understand that the brain’s glymphatic pathway is responsible for clearing harmful wastes – particularly amyloid-beta plaques that characterize Alzheimer’s Disease, during sleep.

As compared to sleeping on your back or stomach, sleeping on your side may help to clear brain waste.

From "Sleep" - "Employing an animal model, Helen Benveniste, from Stony Brook University (New York, USA), and colleagues studied the cerebrospinal fluid (CSF) - interstitial fluid (ISF) exchange efficiency – a marker of the clearance capacity of the glymphatic pathway.  The team found that sleeping in the lateral position (on one’s side) may more effectively remove brain wastes including amyloid-beta, as compared to sleeping on the back or stomach. The study authors submit that: “We propose that the most popular sleep posture (lateral) has evolved to optimize waste removal during sleep.”