By 2 PM, a sleep chemical called adenosine has been collecting in your brain for seven straight hours. The afternoon wall hits even when you skip lunch entirely.Researchers at Loughborough University ran a driving simulator study. They fed one group a small lunch (305 calories) and another a heavy one (922 calories). Both groups drove for two hours on a long, dull stretch of road. Both got hit by the dip at the same time. Their conclusion: the post-lunch dip is "largely unrelated to lunch."Two t