The short and sweet version (and heavily paraphrased) version is:

If you're tired in the afternoon, you only need a literal moment of sleep to feel revived. You can do this by sitting in a chair, holding something in your hand (a key, in this book), palm down, with something beneath it on the floor (a plate, in this book) that will create some sound when hit. The instant you fall asleep, you drop the item onto the the thing on the floor, it wakes you up, you feel energized.