I got an error message when reloading world and I lost everything I’ve done in game. Spawned where I initially created world from Minecraft day 1.

I had so much going on in my world, only to lose it all. I would get this message when clicking on my world. It will say “There was a problem loading this world.” And below that is the “OK” button. I click it and it would take me back to the main menu. I also noticed my player avatar was temporarily gone for a few seconds. During those few seconds, I only saw my Minecraft name, which I know right off the bat is a very bad sign. When I bypassed the warning prompt and loaded my world, I ended up in the exact same state when I first created the world with absolutely nothing. Everything I’ve built was also lost. All of that hard work for absolutely nothing. Well I guess it’s time for me to take another break from the game.........again.