The book explains about the benefits of sleeping enough and the negative consequences of not sleeping enough, based on scientific research.
It also explains how this problem is neglected. For example, a short snippet from the book about driving:
At the highest levels, we need better public campaigns educating the population about sleep. We spend a tiny fraction of our transportation safety budget warning people of the dangers of drowsy driving compared with the countless campaigns and awareness efforts regarding accidents linked to drugs or alcohol. This despite the fact that drowsy driving is responsible for more accidents than either of these two issues—and is more deadly. Governments could save hundreds of thousands of lives each year if they mobilized such a campaign. It would easily pay for itself, based on the cost savings to the health-care and emergency services bills that drowsy-driving accidents impose. It would of course help lower health-care and auto insurance rates and premiums for individuals.
I conducted an informal survey of colleagues, friends, and family in the United States and in my home country of the United Kingdom. I also sampled friends and colleagues from Spain, Greece, Australia, Germany, Israel, Japan, South Korea, and Canada.
0 percent received any educational materials or information about sleep.
(Of course, this is anecdotal evidence, but I don't think there is a question about the extremely low amount of hours schools dedicate to educating about sleep.)
The book also claims the sleep loss epidemic is a large-scale problem:
This silent sleep loss epidemic is the greatest public health challenge we face in the twenty-first century in developed nations.
Insufficient sleep robs most nations of more than 2 percent of their GDP
(With regard to the last claim, the book references RAND Corporation, Lack of Sleep Costing UK Economy Up to £40 Billion a Year.)
I am not an expert in sleep, nor in cause selection, but this problem seems to me quite neglected (relatively to its scale), and at least partially (e.g., educating about sleep, later school start times) easy to solve (relatively to other issues).
I am less certain about its scale relatively to other global issues, but I wonder about its total score (scale+neglectedness+solvability), if it were assessed like other issues in this table by 80k Hours.
Edit: To clarify, by "the sleep loss epidemic" I refer mainly to sleep-deprived people with no sleep disorders. I assumed (please correct me if I were wrong) that sleep disorders aren't the main cause for sleep-deprivation, which means that we mainly have to deal with seemingly-easier-to-change causes (e.g., education, social norms).