Minecraft Crashing and Deleting Worlds

I was using command blocks and minecraft was really slow, I was making a horse that could run fast, after several attempts each speed was the same and very slow. Minecraft got so slow that I xed out and got back in. To my suprise, my world that I have been building on everyday for the last year had been deleted. Other worlds were not deleted but the one that was, was the only one I used. Any idea on how to get my world back? Until then I am not playing, I mean come one, a years worth of work down the trash. Is this how minecraft is and will continue to be for me?