My key to remaining cool is to make yourself extra aware of the situation. It sounds simple, it's not. When you start to feel overwhelmed the best thing you can do is excuse yourself. Walk away from the situation. Look at your watch (or cell phone) and give yourself ten minutes to NOT think about the problem(s). Grab a coffee or a snack and just breath. After ten minutes, think about the situation. Ask yourself if it really is "the end of the world" or take an inventory of possible solutions and why they will or will not work. Whatever you do- don't take immediate action and don't react with hate or anger. You will make brash decisions and ruin your reputation.
You also want to tell yourself to "Calm down." You will need a reminder. It is ok to repeat the phrase to yourself until you can reasonably review the situation and consider the action you are going to have to take- if any at all. Sometimes I feel it is best to walk away from certain challenges. If someone is getting under your skin that day, shut your door. There doesn't always have to be a confrontation.
I hope this advice helps you. I know it has done wonders for me.
Until next time,