Fatigue can be contagious. It's like being in the room when someone yawns. Discovering the sources of your fatigue may be a lengthy process. Even if you work all day, you can perform some simple stretches or take a walk around the block. Get some sun.
Sunlight is very reviving.
Indoor lighting, no matter how bright, doesn't have the same effect. Even on a cloudy day, you get more light outside than inside. If you can only grab a few minutes outside, try skipping the sunglasses for maximum effect. Dr. Hoffman recommends eating lightly. Also, eat less sugar.