I alt-tabbed out of the game and couldn't get back in it afterwards.
The game was present in the taskbar but if I clicked on it nothing would happen even though I could hear it running in the background as if it hasn't crashed. Right clicking on the game icon and selecting gameclient opened up the windows that are in the screenshot here:>
http://i.imgur.com/mUbPRJq.jpg
Closed the game on my own, everything is still working as normal so no panic there XD