I had just completed a response

Went to preview

Foolishly attempted to edit when in that mode and lost everything

Is there any way that I can get it back

Probably a bit late now, but if you have a pc, do ctrl/z to undo any changes, or try hitting the back button if the page hasn't refreshed loaded. Also a good idea to have something like notepad open and periodically save a long post, as well as doing a ctrl/a and then ctrl/c to copy all of the page as you go along.