The video […] explains how sleep cycles work, and how power naps—or those naps that do the most to boost cognitive function during the day—take advantage of the first two phases of your sleep cycle: stage one, where you’re probably “dozing,” or feel relaxed but if someone woke you you probably wouldn’t even notice you’d been asleep, and stage two, where your brain starts to consolidate memories, organize its biological bookshelves, and shuts the brain off from external, non-dangerous stimuli.