You know it's a tough question. You may know about the story of a king who once told his minister "Tell me a single sentence which will make me happy when I am sad and make me sad when I am happy. Otherwise I will kill you! I don't need dull and lazy ministers!" The minister said, "Your majesty! A hard question this is! May I get a day or two to think about it?" "Yes. Tell me tomorrow at the same time as it is now. You may go now. And remember what I'll do if you couldn't answer......" said the King.
Now the minister thinking deeply all the day, visited many scholars. At last a poor homeless man after getting to know about the situation told him, "This too will pass." The minister got his answer and next day visited the king and said, "My majesty. The answer is "This time too will pass!" When you are sad, thinking this will make you happy and when you are happy, thinking this will make you sad!"
This is what I do under such situations. When I am emotionally or physically or timely disturbed I think "This too will pass!" and this arouses in me a hope of beautiful future thus makes me happy in no time. Though, it may not work for all but I have been addicted to it and this is the only solution I prefer to use. My mind has been familiar with it. Practice, practice and hopeful practice will help you as well! Sometimes talking to myself and motivating myself and shedding some tears also work nicely for me!