You could try this: http://www.photoshop.recoverytoolbox.com/... Recovery Toolbox for Photoshop I haven't tried myself, yet, but you could give the free trial a spin and see what happens. I'd be curious to see the before and after if you do.
or
If you are using time machine it does a backup every couple hours, so you can get previous versions that way. As a habit I save my file with a different name every couple hours, just in case a file gets corrupted.