Try switching to a ketogenic (ultra low carb / high fat) diet for a week or two beforehand. The reason you have no focus or energy is due to a lack of glucose

Try switching to a ketogenic (ultra low carb / high fat) diet for a week or two beforehand. The reason you have no focus or energy is due to a lack of glucose (sugar). When you fast your glycogen stores (carbs) will deplete and your body will start running on fat. During the transition, before adjusting, you'll feel slow, weak, and have trouble focusing.