I have found when the system logs me out, I sign in again and then go back 2-3 pages and find the message I had typed and click on either preview or submit, the message is not lost. I have been logged out by the system many times (as I usually have many interruptions when writing a post) and I have not yet lost a message -- as long as I follow these steps.

I hope this also helps in retrieving messages.

Warmly,
DejaVu