According to William Shakespeare in Macbeth, sleep “knits up the ravell’d sleave of care.” As with so many other aspects of the human condition, The Bard articulated a profound truth with that line. To help unravel the myriad of facets appertaining to sleep revealed by the latest scientific research, I spoke to Dr. Raphael Vallat, a postdoctoral researcher in Dr. Matthew Walker’s lab, the Center for Human Sleep Science, at UC Berkley. Yes, that Matthew Walker, author of the best-selling, Why We Sleep, which significantly deepened my understanding of this inordinately necessary physiological process. After inquiring about his background and to reflect on the scientific method, I asked Dr. Vallat why we need to sleep at all. As he pointed out, even though no single dispositive answer to this question has yet been settled upon, it appears that sleep “impacts all the major physiological systems” and is “very important for learning and memory.” We spoke at some length about the stages of sleep, which are divided broadly, but not too imaginatively, into Non-REM and REM sleep. REM, or Rapid Eye Movement, sleep remains something of a mystery and is an active area of ongoing research. In fact, Dr. Vallat described it as “one of the greatest mysteries” and admitted that scientists are still not sure why we have it, although some clues have been uncovered. Unfortunately for those like me who enjoy the odd tipple at night, alcohol is severely disruptive to REM sleep. Other topics we discussed include how scientists know that we need between seven and nine hours of sleep, the nature of chronotypes, the exceedingly rare gene variant that enables those who possess it to sleep less than the average person, whether it is possible to sleep too much, and the function of dreams. The last major topic we discussed was how to achieve better sleep, which prompted Dr. Vallat to provide many helpful pointers. Links: Dr. Raphael Vallat’s personal website: https://raphaelvallat.com/ Dr. Vallat’s Twitter account: https://twitter.com/RaphaelVallat Why We Sleep by Matthew Walker: https://www.simonandschuster.com/books/Why-We-Sleep/Matthew-Walker/9781501144325 10 Tips for a Better Night’s Sleep from the National Sleep Foundation: https://www.thensf.org/sleep-tips/ The STOP-BANG questionnaire (a free screening tool for sleep apnea): http://www.stopbang.ca/osa/screening.php Twitter account for Skeptically Curious: https://twitter.com/SkepticallyCur1 Patreon page for Skeptically Curious: https://www.patreon.com/skepticallycurious