First of all take a deep breath. Now let me tell you what I have tried to focus during exams:
1. If it is day time there, go for a short walk to distract yourself, or do something active i.e. jumping around or doing some aerobics exercises will help because it will use some of your stored energy.
2. Take enough breaks while you are studying. Do NOT study the same topic for your paper over and over again because you will be frustrated! Break it into different chunks, practice past exams and find out what exactly you are weak at. What topic needs focusing and study for that. Then move on to the next topic. Do not study continuously for hours n hours without taking a break. Take a short break (2-3 mins) after 20 mins of study. Break your 1 hr study session into 20 min slots and take a 2-3 min break within each one. AFter the hour of studying, take a longer break which can be 5-10 mins long. You can do anything in this time. Drink tea, eat something, or even some dance. Whatever that pleases you but do not go near tv or your cell phone because you will be distracted and will procrastinate, I know this because I have done it many times myself.
3. After one hour into that first topic, a break and then start with a different topic. This will let your mind feel refreshed not bored.
4. Drink plenty of water to keep yourself hydrated. Remember our brain is ~71 % water so we need enough fuel to let it work.
5. Do NOT starve yourself. Eat some healthy carbs because they help us provide enough energy when we are using our mental energy. Note: we need carbohydrates to focus and understand. So cut down on junk but eat good healthy foods.
6. Sleep. I struggled with this one myself because I could hardly sleep 30 mins before my final. I wish I could give you a healthy tip on this one. But DO NOT follow what I have said about sleep. Try getting some sleep whenever you feel the need of it. Maybe a midday nap could help because our endogenous clock screws up in anxiety so just get sleep whenever you can but do set an alarm on so you can study to the maximum.
Lastly, all the best for your exams. Oh,, one more thing, have a shower it also helps. I washed my head with cold water (for only 1-2 mins during exams) to calm me down you don't have to.