Loss of worlds

I downloaded a custom skin earlier and the result was that my Minecraft reset completely. I lost all my world's, server stats and friends and because I can't successfully back them up on this device, I can't get them back. Is this meant to happen? If so, PLEASE ADD A WARNING SO THAT IF ANYONE DOES THAT IN THE FUTURE, THEY ARE AWARE THEY COULD LOSE ALL THEIR PROGRESS. Also, is there a way I can get my world's back? Thanks and stay safe