I was watching a youtube video when my mac suddenly went to the login screen. It happened fast, just as if I had logged out of my Mac. Upon logging back in, all of my apps re-launched and it was as if it had rebooted. Not sure if this is a common problem or am I the only one with this. Not sure, but this has happened at least once before (at night) but I thought it was because of an update. This time it wasn't.