Extract from “Laughter prescription.” William B Strean

“Findings range from suggesting that, in addition to a stress-relief effect, laughter can bring about  feelings of being uplifted or fulfilled[16] to showing that the act of laughter can lead to immediate increases in heart rate, respiratory rate, respiratory depth, and oxygen consumption. [17] These increases are then followed by a period of muscle relaxation, with a corresponding decrease in heart rate, respiratory rate, and blood pressure.”