EVERYTHING I have built just disappeared as if it was never there. :(

I've been making a mini-games map for me and my friends. About 7 days into creating it, I had a death run, a dropper map, a main hub, a spawn point and a load of commands relating to teleporting, testfor and other bits for the mini-games. I just logged off to go to bed but realised something I needed to do so I logged back on. When it "loaded", it was just the default super flat world. No creations, everything that I had built was gone. I even tried teleporting to a coordinate for the death run and nothing was there. Just as if I had created a new super flat world, but I hadnt because the world was still named the same.     The picture shows the coordinates of where my my main hub was.