I have Pseudobulbar my friend. Which means I have a laughing disorder. I laugh at things that are'nt funny, when people are injured and when I'm in trouble. I always thought I just had a good sense of humour but now I know it's serious. It's not contagious of course, I think it's just genetic.
Here's a link from Wikipedia about it.
I just thought I'd let you know in case we play online and speak to each other and if you say something that's not funny, I might laugh at it.