Don't get excited! or Calm yourself. or Cool it. or Calm down. or Simmer down. or Take it easy. or Take a deep breath. or Control yourself. or Don't let it get to you. or Cool down. or Cool off. or Deal with it. or Keep your shirt on. or Chill out. or Loosen up. or Get a grip . or Don't be uptight. or Restrain yourself. or Don't get all worked up.