Yell a Lot
What this does is let people think that you are, in fact, working. Not only that but working on something so diligently that your computer resources couldn't keep up! Scream that you want to "throw this damn laptop through the window and autoerotic asphyxiate with the remaining Cat5 cabling." This angry act also affords you a quick "cool down walk." No one will question you. They'll actually encourage it. Tell everyone on your way to the break room how much Excel sucks. "Those damn processors" is a thing you can say that sounds convincing. Once in the break room, refill your water (which will help perpetuate more bathroom breaks). It's all about efficiency—just don't be too efficient.