My World Was Deleted.

Hello,

Overall what happened:
I created a new world in private mode at the end of the year 2015. Yesterday, I was playing on the world all day but it became extremely laggy and I had to force restart my laptop. When I relaunched Minecraft, sadly... my world I was working on was not there any more. I don't understand how it ended up this way.

What I expected to happen was...:
I thought my world was going to be there even though my laptop had to be restarted.

Describe what you thought should happen here
What actually happened was...:
My world was deleted. I don't see the world as my choice to work on in the private mode.

Steps to Reproduce:
1. I changed my normal survival level to peaceful right before program crash. I wonder if it triggered the deletion.

My request is to restore the world I was working on. Even it isn't fully up to date, I would like to get it back. I think deletion happened around 1 am (PST) on 1/5/2016. Please help me out.

Thank you so much!