A Three Year-Old Girl, a Colony of Dogs, and One Very Rare Side Effect

When Mathilda Crisp was three years-old, she got sick. She stopped sleeping through the night, but during the day, she would fall asleep without warning — during a swim lesson, for example, or straight into her cereal bowl at breakfast. For one doctor, figuring out what was making this little girl sick was just the beginning of an even bigger medical mystery.