How can I boost my energy in the afternoon at work?

Exercise. If there isn't anything medically or physically impacting you, then evaluate whether or not you have adequate food and exercise. Sometimes eating too much sugar or fat can cause drowsiness. A build up of Lactic Acid can affect energy and exercise to the point of sweating can help reduce this. It is important to move your body on a regular basis, if you are sitting for long periods of time, move.