In some boards it is possible to use the back-button and the browser still has it of some sort. Not here if I recall it correctly. However, if the post is not saved, the board does not know it, hence it is gone.
Some advice for the next time (no, not the copy it advice

): the timeout maybe came due to Your login-options. User login forever, then You shouldn't get logged out. Mabye Your other options within Your net-use do log You out, when there is no event in the browser or something. Check that, too.