5. Dreams involving dangerous and threatening situations are very common, and the Primitive Instinct Rehearsal Theory holds that the content of a dream is significant to its purpose. Whether it’s an anxiety filled night of being chased through the woods by a bear, or fighting off a ninja in a dark alley, these dreams allow you to practice your fight or flight instincts and keep them sharp and dependable, in case you’ll need them in real life. But it doesn’t always have to be unpleasant; for instance, dreams about your attractive neighbor could actually give your reproductive instinct some practice too.