My World that I've played on got deleted when I re-logged into Minecraft

I always made sure when I'm playing a world, I exit out through the menu and wait for it to finish. For some odd reason, I logged back on for it to not show my world anymore. I'm not sure if it got corrupted/deleted, It's never happened to me even though I make sure that the world saves completely. Is there any reason how the world could have deleted?