This is related to this bug: http://trac.wordpress.org/ticket/6715
In trying to redo my lost post (from going into HTML mode), I inserted 2 photos and typed some text. I hit "save" and got the "are you sure you want to navigate away from this page" popup. I cancelled but got it when I tried again. So I cut and paste my post into Word as a backup and then came back to WP and hit "okay."
My text and pictures went away. Gone. Into the ether. Just like with the other bug.
I have successfully done manual saves in 2.5 before. I don't know why I'm getting a false navigation popup or why I lose my post body content but not the title, cats, tags, etc.
Wordpress has become completely unusable now.