Have you tried switching to windowed or fake fullscreen display mode?
If you Alt-Tab out of the game and back, does that reset the graphics?
Have you tried any other, similarly demanding games since this started?
If you create a new profile and start a new game to test, is this still an issue (if it happens frequently enough to make checking in a new game feasible, or is relatively reproducible with explosive barrels, etc, available near the start of the game)?