Any emotion can be contagious, depending on the susceptibility of the recipient (victim?). A chronically serious person who has an attitude against silliness might not laugh at anything, but it might crack a momentary smile.
Most people let environment (including circumstances) control their emotions, but really they are ultimately responsible for their emotional state.
During the summer Olympics several years ago, one of the favorites on the parallel bars slipped and fell. That rattled nearly everyone. Scores plummeted. Everyone except one young woman from the US suddenly did poorly. That one young woman had the faith to pull her above such contagion.
I experienced such "rising above contagion" on a number of occasions. Once, feeling pretty bad (depressed) over life and circumstances, I suddenly realized that I was in that state and vowed to get myself out. I forced myself to smile. That didn't do it, so I forced myself to laugh. I continued to laugh a gusty, full, belly laugh and felt my body relax. Suddenly, I was not only happy, but exhilarated.
Another time, in traffic (rush hour, bumper-to-bumper, L.A.), I felt extreme frustration mount toward rage after six reckless drivers cut in front of me dangerously close. If my reaction time had not been so good, they would've had damaged vehicles. When I realized that I was 100% responsible for my frustration and their intrusions, I was no longer a victim. What happened next was nothing short of a miracle (Edit [Moderator]: Link removed
Falling for a fit of laughter sounds like a lot of fun. I've experienced that on a number of occasions. But consciously controlling your own emotions is about ten shades more cool.