Logged out of OS X?

I left steam running and my computer open and logged in and went to run an errand.

I came back to the lock screen, typed in my password, and then was kicked back to the login screen to log in again... Now I cannot launch steam.

Restarting now, but wanted to log the occurrence.

http://imgur.com/tV0ao,kKU3R#0
http://imgur.com/tV0ao,kKU3R#1

 

Bumping, just happened again, in the middle of a YouTube video, while connecting my external display.

----------

It also cleared my cookies..

I got logged out of all the sites I was logged in to