Crash on second player entry that deletes the world

While playing on a game I have been playing for a few days now alone building in creative mode, a friend tried to join the server. The joining caused a major lag spike that is not typical in our survival games that we frequently join each other in, followed by a crash of the game and the laptop shutting down. When rebooted my primary skin was booted back to the default skin and the world I had been playing in was erased from the game screen and no traces of it could be found when delving into files.