Well, it's kind of hard to say. Sleep paralysis isn't that well understood, and neither, for that matter, is laughter.

I wouldn't say anything too abnormal is going on, though. I mean, I saw a thread recently where people were talking about their experiences with waking up crying. Laughter shouldn't be a whole lot different...

But hey. As long as you aren't getting up and sleepwalking, like sleep paralysis is supposed to prevent, I'd say your brain and body are working just fine.