Several things...
1. if you clear cookies (or some protocol clears them in the background) you may have to login again.
2. Check the "remember" me box on the way in - it helps.
3. if you stay connected to the site, the server will sever your connections after an idle period (I think 50 mins) BUT as soon as you hit a hey, it will be restored unless your login cookie has been purged.
4. many browsers and security apps, purge cookies unless you specifically tell them not to.