the singleplayer world crashed and lost problem

my minecraft magic launcher have been crashing for quite some time but now my single player world is crashing whenever i try to get in and suddenly my world that has my big medievil project dissapear and i cant find it even in the save

What I expected to happen was that i deleted a world and that world that have my medievil build in it but when i went to saves and tried to recovered it and so i went to properties and its not there.:

What actually happened was sorry but i really dont know and thats why i need your help, i was so dissapointed and frustrated cos i spend weeks and hours making that world and it just suddenly dissapears with no reason so i need your help MOJANG but the servers are still working.
Describe what happened here

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. whenever you try to get in creative and survival it crashes
3. ...i am sorry mojang not having enough steps on how to trigger the bug.
thank you
from minecraft- Masterexplorer7 and i dont have the folder sorry but you can just email the solution to my email thank you