screen with yellow filter and blurry edges?

[plus300]

So guys, I just finished cleaning up all the side missions before the story mission "this ends here", I enter my player menu to check the new challenges, click esc to go back to the game and BAM:
my screen is now yellowish, the edges are blurred, my character seems to be walking a bit of in a slow motion and my UI (minimap, health bar, etc.) disappears! It lasts for a couple of seconds and then goes back to normal.

What did I just trigger and how?

[plus300]

I feel stupid, just had to press "Q"...