Since the summer of 2008, Louisa has been slipping into a deep sleep roughly every four to eight weeks. Once she falls asleep, she stays in this state for up to two weeks at a time. She has to be woken twice a day by her parents to take food and go to the toilet. The sleep episodes come on her over the course of a day or so and her family have learned to recognise the warning signals: Louisa gets moody, her face flickers with faint spasms and she becomes unresponsive. 24 hours later she is in the grip of a full-on sleep episode: her school work piles up, her Facebook page lies dormant and the world goes on without her.