When I pressed "Submit" on the bulletin board, I lost my post. How do I get it back?

You can't - really. A helpful tip when posting on line is to remember that the browser is really fragile - and the web itself is held together with duct tape and old glue. 

The next time around, write your post in Apple "Notes", or an editor of choice, so that you can spell check it, craft it, and most importantly … save it.