Ever been madly typing away and getting ready to submit, somehow you selected everything you typed, then you hit a keyboard key and everything disappears?
Don't touch another thing, then carefully do a Control Z on your keyboard.
You might be lucky.
Another tip, if you have typed a long post, before submitting (in case there's a glitch), select all (Control A) and copy it to the clipboard (Control C)
Then if the submit fails, you can use the back key in your browser, but if there's a problem you can also paste to Notepad or something.