How to energize myself ? always feel a bit dull and sleepy at work

Avoid sugar, caffein: Regular exercise, getting enough sleep, avoid sugar and caffeine, open window if you can. It could be due to sick building syndrome - lack of proper air circulation if windows are sealed closed. Get up from your desk every hour for a stretch or a short walk. If you are a vegetarian, vitamin B12 supplementation can help. A multivitamin and coq10 could also help. Or, perhaps your job is boring.