Insomnia is a growing problem in Britain, but not just for adults. Children are getting less sleep than they used to. One in five parents believe that their children are not getting as much sleep as they should. Science still can't fully explain what happens in our brains at night and there are a number of reasons why children don't sleep properly.

This Cutting Edge film reveals what life is like for a little girl whose insomnia has become more than just a childhood habit. Three-and-a-half-year-old Jess has a condition that has baffled every doctor she has seen so far.

For the last two and a half years she has been living a double life: during the day she is a bright and happy girl but at night she is 'different'. Then, Jess spends hours sitting in a trance, acting out elaborate scenes. She describes the 'friends' who come to visit her, who keep her awake, who hit her and who won't go away.

The problem could be sleepwalking, night terrors, sleep apnoea or any of the well-known sleep disorders, but nobody even knows whether Jess is dreaming or awake. Whatever the cause, she is getting less than half the proper sleep she needs.

The last time Jess slept in her own bed she was 11 months old. Frightened she might move around and hurt herself, Jess's parents, Chris and Tanya, let her crawl into bed with them. With school starting next year, there is growing concern that Jess's health will affect her ability to learn properly.

They've tried everything they can think of to get a good night's sleep, but nothing has worked. And they're getting desperate and as tired as Jess. With her soldier husband Chris heading for an eight-month tour of duty in Afghanistan, Tanya finally turns to the sleep clinic at the Evelina Children's Hospital in London.

Jess is monitored at home and then observed at the clinic to first ascertain if she is sleepwalking or awake, or if her condition is even rarer still. But can even Britain's top paediatric sleep doctors unravel the mystery of Jess's night-life?