Well it's funny here because of the video game tie in, but I don't find it all that hard to believe. Back in college they covered subjects like how trauma, especially head trauma, can cause radical physical effects and personality changes. Granted it's usually negative, but apparently there have been situations where people have been smacked in the head or even had their brain penetrated by steel rods, and then wound up being able to speak a foreign language they had been indirectly exposed to fluently. More frequently though you have people turn violent, and/or suffer from other disorders. I supposed Nymphomania isn't that hard to believe.
All I can say is that I have brain damage and it's affected me profoundly over the years. When it comes to the brain people know a lot less than we'd like to believe, and even when a problem is understood there generally isn't much that can be done about it.
All fiction aside though Nymphomania is a serious problem not "fun".
In this case you can't blame the Wii Board, I mean there is a warning about the falling risk and it's an injury like any other in the final equasion. Still, if this is serious (which I doubt given the source, despite my claims abouve about the probability) I'd think it would be decent PR for Nintendo to offer some help in this case.