Yes I would say so. I do it after I've failed to say a word due to having a speech block. I think laughing or smiling in dire or uncomfortable situation serves to diffuse the tension and make things less serious. I guess that's the role of good comedy. I tend to involuntarily laugh or smile when I'm nervous or uncomfortable anyway. Sometimes it's inappropriate to do so especially if you hear that someone died or something. But it's not something I can help.