How can I stop losing my screens when I close the lid? When I close the lid of my MacBook Air, it's almost always plugged in.  When I open the lid, I have to sign in and my screen is clear of all the things I wanted to see or was looking at, but did not finish.  This happens several times a day.  I have to close the lid because of a possible dust situation where I need to keep the computer during the day.  This just started happening a couple of weeks ago.  I am running OS X El Capitan.  I do not log out, but it thinks I did.  Grrrrrrr!
Sounds to me like the cause of it is this setting, which you'll want to disable:

System Preferences &gt; Security &amp; Privacy &gt; 
Require a password X minutes after sleep or screen saver begins