You climb into bed after a long day, close your eyes, and slowly sink into relaxation. Then, without warning, your body suddenly jerks. For a split second, it feels as though you slipped, tripped, or fell from a great height. If this has happened to you, you are far from alone. Scientists estimate that nearly 70 percent of people experience these mysterious sleep twitches at some point in their lives. They are called hypnic jerks or sleep starts, and despite how dramatic they feel, they are usually completely harmless. The fascinating part is that experts still debate exactly why they happen. Some believe they are connected to the way the brain transitions into sleep, while others think they may be leftovers from ancient survival instincts that helped our ancestors avoid falling from trees. Here is what science knows about one of the strangest things the human body does.
