You must have read reports here and there, in newspapers or magazines. I can confirm it. When you are really, really sad, and nothing seems to be going the way you desire, eat chocolate. Not too much. Just a tiny bar. You will see tangible change in your mood. I have tried it on myself and it works. Caution: it does not change the mood permanently. The trick is to immediately set yourself a virtuous cycle that keeps you there. The moment your mood starts on its upswing, start doing things that makes your mood even better and better till the symptom (sadness) disappears. Warning: Chocolate will do nothing to remove the root cause of your sadness. You have to find a cure for that yuourself.