Take short breaks every 1 hour or so. You could go for a cup of coffee or just take a bathroom break. If your office is in an area where you can enjoy greenery or take a stroll, you can always go for one. In fact, I encourage you to. When we walk, endorphins are released which relieves our stress. If these still don't work, maybe you need a change of atmosphere. You could ask your supervisor to change your cubicle, or ask to be assigned to a different project. You could even try your hand at something else, if your work permits you to. You could call me if you need more tips to overcome this situation.