How do i stop nervous laughter?

I volunteer at a care home for the elderly. I was sitting with a patient and talking to them when suddenly they started coughing, obviously food had gone down the wrong way and they were trying to cough it back up. I couldn't help it I just laughed until I was sweaty and red in the face. I wasn't laughing at her, I was laughing because everybody else in the room (like 20 people) were staring and there was just silence apart from her coughing noises. I got told off by one of the care assistants and she said "don't laugh" really loud in front of everyone so that made it a hundred times worse. I need to stop this, I'm almost 18! How?