First of all, it may be the symptom of some illnesses. If you're sure you're ok, try cutting out eating too much, spend more time outdoors. If you work hard, your brain definitely needs some brain boosters to work productively. A really cool thing that helps me to be active throughout a day is taking cold shower in the morning. It really helps to wake up) Also, try to eat nuts and 1 apple before sleep. Also, a good way to overcome your state is walking as much as you can.