I was sneaking on Snow Blocks at Y=255 at Day with clear weather in peaceful mode while making a pixelart. Eventually I died. I got the message fall from a high place, but when I built the pixelart I even never jumped! I also had full health and because of peaceful mode, no elytra. I also played in single-player. And yes, I died eventually with 10 hearts instantly, like someone had one-hitted me with a enchanted netherite sword or simple /kill ed me. But this world is single-player so this isn't the reason. Unfortunately I have no screenshot but I hope that this is enough explanation.