See the light. SAD is a mood disorder triggered by the reduced daylight of winter and is responsive to treatment with light. So for your afternoon slump, try natural light treatment by bundling up and taking a brisk midday walk. Especially if done regularly, this combination of light and exercise is likely to boost your energy and alertness. Take an exercise break.
Exercise is good for renewing energy and spirit.
First, inhale and push your shoulders forward as if you're collapsing your chest. Then, lift your shoulders up toward your ears. Next, squeeze your shoulder blades together as you begin to exhale. Finally, drop your shoulders and release the tension, exhaling completely. Repeat once or twice.