I have 120 fps and suddly i have 5 fps!

[xSurvimanx]

I'm from Poland, so my english will not be perfect.   I have 60 fps and suddly i have 5 fps on ultra, low, medium and hight settings! In BF3 i have 60 fps on ultra. It's very annoying because when i turn back it's lagging and screen is freezen for about 3s