While I was randomly playing in my survival singleplayer world, I was going to climb some stairs to my base which was in a ravine. before I could go, I got hit by an invisible entity. I have seen some people report that and their problem was an invisible mob or something, but when I looked behind me, I was able to see the sweep effect caused by a sword hit, so that's a bit strange. and I haven't gotten hit at all afterwards. Is this a common bug or what?