In situations of imminence, some murderous sects would turn off the emotional side of the brain with meditations they used to teach the mind to activate certain mental states and deactivate others with a word switch. It's not too difficult either, but I don't want to provide knowledge of an Islamic murderous sect on a forum sincerely.
One thing you can do is first to learn how to control and govern your emotions. This is done with void meditation that teaches you how to manage what is going on in your head. In combat situations, I have often had to face opponents who are stronger and more trained than I am. Laughing relieves nervous tension.
In addition, an opponent who is trying to demonstrate his power will be humbled by noticing that you in front of his imposing brutality are laughing. Laughing in itself relieves tension and puts you in the right mood when you have a problem.