I have an alright computer, and I have always been able to run Minecraft on far and fancy with no lag, however, since a couple of days ago, I get crazy amounts of mob and block lag, even when everything else is running perfectly well. I'm using short and fast rendering now, and getting around 65 FPS, and all seems well, until you look at the mobs and the blocks I break, then you would think I was playing out of a microwave. Can somebody please tell me what this is and how I can fix it?