Users will automatically be logged out if there is a period of inactivity which extends beyiond the default value of 15 seconds as configured in:
Global Configuration>System>Session Settings>Session Lifetime= 15
You may wish to extend this value to say 30, especially if you find that you may be losing page updates through extended periods of inactivity due to coffee breaks, watching Coronation Street, etc :>)
If you're writing a Joomla article, it appears that any keystroke will refresh the timer and keep the session live. However, after any significant input of text it may be prudent to click on either APPLY or SAVE to preserve your efforts.
If you're writing a Mass Email, then it appears that keystrokes will NOT refresh the session timer...and there's no facility to save your work either.
So, if you want to take your time composing an email, we suggest using Notepad, Wordpad or any other text editor to put your message together in advance. When you've finished, you can then simply cut-and-paste your message into the Mass Email text area and send it in a timely fashion without fear of losing your work.
If you're writing an article and you suspect you have exceeded the life of the Session Timer, hitting Save will simply log you out and you'll have to begin again. Our experience as shown us that if you hit Apply instead, this seems to ignore the session time and will let you save your work. It also appears to reset the session timer. This may be because there is something peculiar to our own Joomla set up. We're not absolutely sure. However, it's worth a try and could save you doing a re-write.