Again, Dement doesn't argue against this. There is a tendency to get tired in the afternoon, because clock-dependent alerting (which give us our diurnal sleep s

Again, Dement doesn't argue against this. There is a tendency to get tired in the afternoon, because clock-dependent alerting (which give us our diurnal sleep schedule) dips at that time. But he's arguing that the reason this is affecting people so strongly is because basically everyone is chronically sleep deprived.