[1][2][3] Walker spent four years writing the book, in which he asserts that sleep deprivation is linked to numerous fatal diseases, including dementia.

[8] Walker's communication style, in which he makes use of "metaphors and analogies effectively," allowed him to explain ideas related to sleep in detail.

[3][9] At 18 years of age, Walker, who was a medical student at the time, became an "accidental sleep researcher" and moved over to studying neuroscience because of his habit of asking many questions.

[8][11] The book is written from a neuroscientific view, mainly devoted to discussing the impact of sleep on the functions of the human brain.

[7] Also explained by Walker is why adults who sleep for less than 6 hours at the age of 40 and over, have a higher chance of suffering a cardiac arrest or a stroke during their lifetime.

He goes on to address the PTSD victims' nightmares, stating that their dreams' ability to heal them by easing the emotions connected to a distressing memory, is affected by a larger quantity of noradrenaline being created.

Walker also believes that dreams carry information regarding fundamental emotions, while admitting that they can be quite apparent, resulting in no explanations required to describe them.

This resulted in the volunteers being "cognitively impaired" along with their brains being heavily damaged, regardless of the three week eight-hour sleep schedule they received later.

[13] Walker wrote that research proves that sleeping after studying allows for "memory, integration and retention benefits" to occur.

The impact of caffeine on sleep is in the book, with Walker noting its effects on the adenosine that allows people to fall asleep.

[11][18] Why We Sleep has garnered a generally positive reception from critics, with Walker admitting to not knowing his book would be a hit amongst readers.

[26] Kylie O'Brien's review described the book as "beautifully written" and filled with scientific facts that clarifies the question its title asks.

[27] A review from Alexey Guzey, an independent researcher, criticized the book in an essay entitled Matthew Walker's "Why We Sleep" Is Riddled with Scientific and Factual Errors.

[30] In a later post on Columbia's statistics blog, Gelman indicated that Walker's purported removal of a bar from a graph could be a "smoking gun," commenting that it entered "research misconduct" territory.

[26] Anu Valtonen voiced her concern regarding the speculation the book makes when taking a neuroscientific stance on the main insights into how sleep and dreams function.