It started in a bedrock level mine. When moving up or down blocks or steps we were getting hit 5 or 6 times, without any enemies around (empty hallways). When we die it says that the Player fell from a high place. Then it started to happen in towers, and today it happened out in the open. Always when moving up or down a level. Sometimes when we die all of our equipment and food is gone, sometimes we can recover all of it. We haven't lost any experience yet.