GREEN BAY, WI — In preparation for an early work day, local man David Miles drank a cup of coffee so that, in addition to feeling tired, he could also be irritable. "The caffeine really helps," Miles said as he prepared for a busy day at the office. "Now, I don't just feel tired, but also jittery and easily frustrated by everything all day." Miles, who works at a major insurance firm in the area, has been described by his managers as a loyal employee who frequently shows up to work on time despite being tired and irritable. "About...