My world stopped working

The error you are getting seems to be similar to a Chunk Loading Error but on a major scale, this can happen if the memory you have assigned is nearing its maximum capacity or your connection to a server is bad. (This is ruled out however as you are not connected to a server)

I would suggest checking if you can assign any more ram to minecraft.

• Check how much RAM your PC has.
• How to assign more RAM to minecraft

If you cannot assign any more RAM then i would suggest changing certain settings, such as view distance, texture quality (clouds, grass, water etc). I would also suggest installing optifine:

• How to install optifine

And if all that doesn't work, it may be something such as entity lag. Using the /butcher command will kill all nearby mobs and may free up some memory in order to load the chunks nearby.

Hope this helps.

References: Previous experience, Minecraft wiki.