It's late afternoon and I'm sitting in a consulting room deep within the labyrinthine corridors of the Queen Victoria Hospital in East Grinstead, watching a man learn whether the sleep disorder that is seriously affecting his quality of life can be treated. It's quiet and consultant Peter Venn's reassuring timbre and the view of rose-bordered lawns through the window are, ironically, conducive to sleep.

The patient, initially upbeat, becomes more taciturn when trying to explain to Venn what's going on. His wife gently places her hand on his arm to offer reassurance, before explaining what her husband is really going through. He has such bad headaches he can't sleep, she says, nervously smiling as he slowly nods his agreement.

Venn, a sleep disorder specialist who set up the East Grinstead Sleep Centre in the early 1990s, says a patient's sleeping partner will always tell the truth about what is happening. "It's often the wife or partner who will be able to say, 'Oh, he kicks wildly' or 'He snores terribly' or 'He stops breathing completely'. The patient will often not be aware of it."

Conflict can arise in the consultation room and Venn says he has seen people who are on the verge of divorce. "I've had scenarios where I've had to be the arbitrator in a marital dispute, but it's fascinating.

"If I go to a party and tell them what I do, you can guarantee I'll have a group of people around me every time. People think there's a bit of voyeurism to what we do, that we probe into what people get up to in the bedroom. We do – though only in clinical terms – but you can guarantee it will spark a conversation. It's good for breaking the ice. It's what I call sexy medicine."

By training, Venn is an anaesthetist, following in the footsteps of his father. In 1985 he became interested in sleep medicine. "It was in its infancy, no one knew about breathing and sleep back then, snoring was treated as a joke and nobody realised there were medical implications."

When Venn arrived at the Queen Victoria as a consultant anaesthetist in 1991, he set up the unit with a single patient. Now it gets almost 2,000 referrals a year and employs 20 staff. "It's my baby and my legacy to the NHS," Venn says proudly.

I sit in on a consultation with a middle-aged man who is sleepy during the daytime, snores to the point where his wife wears earplugs, and soaks the bed through excessive sweating. He is found to be suffering from sleep apnea, his oxygen saturation levels falling during sleep. This is affecting his heart rate, which is rising and falling instead of remaining low and steady.

Venn patiently questions him on everything from dreaming and nightmares, dry mouth, headaches, panic and anxiety, right through to his hobbies and caffeine intake. The man had previously suffered an undiagnosed heart attack, making his condition particularly troubling. Venn recommends he is fitted with a "C-Pap" breathing machine and mask during the night, a treatment used by half his patients. It is essentially a glorified air compressor - the pressure keeps the throat open so that patients can breathe naturally.

I mention that I'm told I snore occasionally. Venn explains that it's the breathing quality that determines the difference between routine snoring and a sleep problem.

"If you just make a little noise at night, and have no daytime sleepiness and there is no change in your oxygen saturation levels, then you technically do not need any treatment from a medical point of view," he says.

"If the breathing is compromised, which it very often is, then you start to get changes to the amount of effort needed in order to breathe. If the muscles are having to work twice as hard they'll send messages to the brain which disrupt normal sleep."

At around £350 each, the 7,000 C-Paps being used by Venn's patients have cost a shade under £2.5m – cost-effective, he says, because, further down the line, many patients will avoid expensive cardiac treatment. "I'm convinced that the recent reduction in cardio-vascular incidents in this country is related to more patients being treated with C-Pap machines. There are people alive, who would not be alive if they had not been treated by us."

Venn's mobile pings every few minutes with an email, and he confides that he has about 600 in his in-box at the moment. He thinks the growth of email and other factors of modern life has, in part, led to a rise in sleep disorders.

"Modern life isn't really conducive to good sleep. I wake up a lot on a Saturday night and think about all the things I have to do. I tell my patients they must put the light on, write down whatever the problem is, put the light off and go back to sleep so that they know the problem is parked."

Venn says the typical patient is an "overweight, middle aged bloke" suffering from sleep apnea. But he also treats narcolepsy (when someone's sleep/wake switch doesn't work properly so they fall asleep during the day); obesity hypo-ventilation syndrome (where patients are very overweight and cannot breathe in or out properly, leading to a lack of oxygen, as well as carbon dioxide remaining in the body); and parasomnias, such as sleepwalking, sleeptalking, and confusional arousals ("where people wake up still confused from sleep and see their wardrobe turning into a giant spider").

Dream enactment is another recognised condition, which occurs when the brain fails to paralyse a person's muscles properly during dreaming sleep. Venn says sufferers tend to be middle-aged men and the dreams are often violent – they can hit their bed partner in the face or fight them.

"I've had women come in with black eyes and bruising because they've been hit accidentally," he explains. Dream enactments can possibly herald the onset of Parkinson's disease, Venn says, saying there is a neuro-degenerative association.

Venn used to have to split his time between his work as a consultant anaesthetist with his growing work as a sleep medicine specialist, but he now only performs work in anaesthetics on a Saturday.

On a weekday when he is in the sleep clinic, he will begin his day reviewing videos and notes from the previous night's sleep studies, undertaken by his team of skilled and diligent sleep technicians, with up to six patients a night staying at the centre to be analysed.

I take a look at the rooms and they appear spacious and comfortable. The medical apparatus is not overly obtrusive, and Venn says many patients sleep as well as their condition allow them to. We watch some videos of patients – many display kicking legs and some alarmingly stop breathing for long seconds at a time before erupting into life with a loud snore and a start.

Patients arrive at about 9.45pm and are monitored all night until around 6-7am, and Venn will review the technicians' notes to help form his diagnosis. He starts his medical clinics at 9am, running through the morning and afternoon in half-hourly appointments. Aside from general sleep problems, he also runs special insomnia clinics. While many people with sleep disorders do not sleep well at night and struggle to stay awake during the day, insomnia patients do not sleep during the night or day.

The latter are treated with psychotherapy rather than physical treatments. The insomnia clinic sees a lot of teenagers with delayed sleep phase syndrome ("I call it 'can't go to sleep at night and get up for school in the morning' syndrome), which can be treated with drugs such as melatonin.

There are networks of doctors and clinics around the country that deal with sleep problems, but some are tiny and unable to cope with the number of referrals. There are about 15 NHS sleep centres that are set up to do full overnight analysis of patients.

Venn takes patients from most of Sussex and as far afield as Kent and Surrey. The insomnia clinic is almost unique in the NHS, and therefore has a much wider catchment area – there are even referrals from Leeds and Scunthorpe.

Venn loves a metaphor – the throat is like the River Thames, with 1.2bn gallons of water flowing through it, but in patients with sleep apnea it's like putting the same volume of water through a small gully. Sometimes the throat is likened to a polo mint. It all helps to put patients at ease.

As I leave Venn's consulting room, I touch the glass head on his desk to which the C-Pap mask is attached.

"I had a bloke the other day who asked how on earth he would get his own head in it – I had to point out that the glass head was just there to demonstrate the mask," he says with a laugh. I suddenly realise that just knowing there are people like Dr Venn around to look after us, will help me sleep a little easier at night.