Based on what you've said
here, it sounds like since you were working on the post for a long time, the board automatically logged you out and the post was lost. It happens sometimes, and isn't something we have any control over. Sorry.
(Trust me, I've been burned by this kind of thing before!)
Sometimes if you've been writing a post or a PM for a long time it's a good idea to copy/paste it into Word or Notepad before you hit the Submit or Preview button.
EDIT: Oops! Hiya, Fantasysci5.