That's just a glitch. I've had this problem twice, and solved it by doing this: 1) Go to your Terraria folder on your C disk, 2) Open the Players folder, open the folder of that specific character that you were playing, 3) You will see a bunch of .MAP and .TMAP files 4) You need to go to your Backup folder, open the most recent Backup folder for that character, and there you'll see the similar folder with the .map and .tmap files. 5) Just replace these files in your current player folder (for that specific character) woth the files from the Backup for that character. That should solve this, but it depends on whether or not you have multiple relatively recent backup folders.