How do you deliver bad news to a patient without laughing?

First and foremost, I don't mean laughing as in I think it's tunny. I tend to smile or laugh when I'm nervous or stressed. It pissed me off because truly it does not mean I find the situation amusing. Sometimes when l've had fights with my mom or friends in the past, l'd just start laughing halfway through and they'd think I wasn't taking it seriously but I was, I just had this sudden urge to laugh that is incredibly challenging to mask.

I’m an EMT, and my biggest fear is losing a patient, and then having to tell the family and accidentally laughing out of nervousness. So far, I haven’t had that happen throughout patient interaction, but it’s something I’m afraid might come up under extreme situations.

Anyone goes through something similar? If so, how do you get past it?

EDIT: I’m reading through all your comments and there’s really good advice there, thank you all so much I really appreciate it!