How to recover lost files?

I was writing up an extremely important document, and regularity saved it to the same folder, and saved almost after every sentence.
I saved the file, closed the application, then turned my Mac off. When I had opened it next, libreoffice gave me the recover document message, and recovered one file, however my other file had gone missing. I searched for the document all over my Mac, but it was as if I had never written the document. I restarted the computer, and opened the application again, and again it was there on the recovery page, but again it was gone.
Advice please.
P.S. I own an Apple MacBook Pro, and the file was an odt.

A) Did you look for a .bak file in the backup folder of your user profile?

B) You might stop to stir your harddisk and try a recovery software as mentioned in this thread.

If you need additional advice, edit your question to ask for it in detail, please.

I keep my fingers crossed.