Nancy, a theatre student at the University of Bedfordshire, hasn’t had an uninterrupted night’s sleep for years. Picture: Pixabay

When she agreed to allow a camera into her bedroom to record what happened once she’d settled down for the night, Nancy Lewendon knew it would make interesting viewing.

She wasn’t wrong: within a couple of hours of the camera rolling, Nancy, 20, can be seen springing up, scrabbling at her bed covers and muttering with panic, her eyes wide with fear as she stares, terrified, into the corner of her  bedroom.

What is she seeing? "It’s usually spiders, or snakes," says Nancy. "It’s like you’re hallucinating: your eyes are open and you think that it’s actually happening but it’s all in your mind." At worst, these cruel nocturnal awakenings can happen three times a night.

That, combined with Nancy’s propensity for sleepwalking, means she hasn’t had a good night’s sleep for years. "I’ve just got used to being permanently tired," she says.

She is not alone. People like Nancy though, suffer from far more extreme versions. It’s a phenomenon examined in a new documentary series, which tries to address why something that should come naturally can prove so impossible.

Those taking part suffer everything from nightmares and narcolepsy to chronic insomnia and sleep paralysis, a condition where sufferers are temporarily unable to move.

All are unanimous that lack of sleep blights their lives and are so desperate to regain a sense of normal nocturnal behaviour that they agreed to have their night-time activity monitored and to compile a sleep diary before subjecting themselves to a night in a sleep clinic, set up for the show.

It used specialised equipment to analyse everything from their eating and drinking habits to their nocturnal brainwaves.

As artist Izzy, 20, who also suffers from night terrors, says: "It’s a terrifying question to ask yourself: 'Will I ever be able to sleep?' "

But it’s a question consultant neurologist and sleep expert Dr Guy Leschziner is trying to answer. He runs the country’s premier sleep clinic at Guy’s and St Thomas’ hospital in London, and believes that everything from an individual’s psychological state to their environment, offers vital clues to the root of the problem.

"A bad night’s sleep can be caused by what’s going on in your mind, your genetics, or even the state of your bedroom," says Dr Leschziner.

"By looking at this whole range of factors I believe we can alleviate or even cure the most debilitating of sleep disorders."

Nancy, a theatre student at the University of Bedfordshire, hasn’t had an uninterrupted night’s sleep for years.

"There’s not a time that I can’t remember sleepwalking," she says. "Sometimes it happens up to three or four times a night. I’ll wake up and I’ve been moving around my room. I don’t always remember it. There have been times when I’ve looked for my laptop in the morning only to find it in my underwear drawer."

At home in Corsham, near Bath, Mum Jo and Dad Guy would often hear Nancy wandering around in the early hours.

"I once tried to go to the toilet in the laundry basket but luckily my mum found me just in time," she says. Jo and Guy have spent hundreds, if not thousands, of nights coaxing their sleepwalking daughter back to bed.

The following morning, they would take it in turns to tell her: "You were messing about in your sleep again last night."

"That was the strangest feeling," Nancy says. "So weird — and it still is — because it always makes me realise I’ve been completely out of control. When I watched some of the footage I was really shocked — it was nerve-racking to see myself acting like that, but completely unconscious. It made me fear what else I could do without knowing."

That Nancy has continued to sleepwalk beyond her teens is unusual. One in three of us does it at some point in our lives, but most stop in childhood.

Sleep technicians, who monitored her overnight, reported their findings to Dr Leschziner.

In Sussex it is a similar scene for Izzy, 20, who, like Nancy, suffers from night terrors. In her case they usually manifest themselves as "black, gothic demons".

"They start ripping flesh at my legs, at my skin, biting into me," she says. "I can’t put across how real it feels."

Now 12 years in to these nocturnal horrors, Izzy has turned to extreme measures: too frightened to go to bed, she forces herself to stay awake for days before collapsing from an exhaustion so intense that she sleeps through the following day and  night.

"The longest I’ve ever slept is 46 hours. My dad had to come and wake me up to make sure I was still alive," she recalls.

Then, whenever she strives to follow a normal sleep pattern the night terrors unfold again, triggering another cycle of avoidance and collapse.

The sleep deprivation — and the psychological stress of worrying about the terror — has had a huge impact on her life.

"I have a headache like the hang-over from hell," she says. "Sometimes I’m so tired I feel sick." Worried father Philip says his daughter is "like a zombie"much of the time.

"It’s really scary," he says. "She’s severely fatigued."