It's an old dance injury.

[mrissa]

One of the hazards of enrolling your child in dance classes is that 27 years later, she may be trying to get her vertigo-induced nausea to settle down enough that she can sleep, and she may be doing other things and concentrating hard on other things and find that, without planning on it, she is singing, "All I want is a happy hippopotamus to keep me companeeeeeeeeee."

You can be forgiven for not foreseeing this terrible eventuality. But some experiences stick with you for life, and apparently the happy hippopotamus song is one of them.