How often do you wake up tired after a full night's sleep?
How often do you find yourself drifting off after lunch? Or while sitting in a meeting? While reading or watching television?
Are you likely to sleep if you lie down in the afternoon? What is the chance you will doze off when you are a passenger in a car for an hour or so? What if you are driving?
When Auckland sleep physician Dr Andrew Veale puts those questions to a middle-aged audience, he gets a forest of upraised arms. They are surprised he tells them none of those tendencies are normal.
Daytime drowsiness may be common, he says, " but common does not mean normal".
All sorts of things can stop someone sleeping through the night: anxieties, entertainments, shift work, burning the candle at both ends. But there is one form of sleep disturbance that is not easily explained or fixed.
It is not insomnia. You are not consciously awake when it disrupts your rest. It is your breathing.
Studies suggest between 2 per cent and 4 per cent of the population suffer from sleep-disturbed breathing. Some of them stop breathing for a period until their body takes emergency action.
Each time this happens - and it can be hundreds of times a night - the normal phases of sleep are disrupted and the person wakes in the morning feeling weary.
Veale explains that the human airway is flaccid tissue. Every breath requires a co-ordinated interplay of many muscles in the throat to keep it open.
In some people the muscles do not work properly during sleep for reasons that are still under study. Their airway collapses, either partially - which causes snoring - or completely, blocking the passage of air for anything from 10 seconds to a minute or more.
The complete blockage causes a medical condition identified in the 1960s and given the name obstructive sleep apnoea syndrome.
About 4 per cent of middle-aged males are thought to suffer obstructive sleep apnoea. It is much less common in women. Maori have a higher incidence of the problem.
Most sufferers are unaware of it. The majority of cases are undiagnosed and untreated, according to the Thoracic Society of Australia and New Zealand.
It believes excess weight is both a cause and a consequence of apnoea. In a 2006 submission to a health committee of inquiry into obesity, the society cited evidence to link the disorder with cardiovascular diseases, heart failure and diabetes.
When apnoea occurs, the body stops breathing for an alarmingly long time - alarming to an observer such as a spouse lying awake.
What is happening, Veale explains, is that the obstruction has caused the sleeper's blood oxygen level to start dropping. And the body's effort to draw in more oxygen causes the heart rate and blood pressure to rise.
The sleeper would die if the brain did not eventually resort to a release of adrenalin that revives the throat muscles, forces him to draw a breath and awaken momentarily.
The arousal is so brief the sleeper is seldom aware of it, though an observer will see the body jerk and hear a sudden, snorting, gasp for air.
Every time this happens the sleep pattern is disrupted and the person is likely to wake in the morning with a sore, dry throat and feeling dog-tired without knowing why.
The interruptions of the body's oxygen supply during the night might be doing more lasting damage to the organs. Obstructive sleep apnoea is thought to contribute to inflammation of the arteries, which predisposes a person to a heart attack or a stroke.
The treatment of sleep-disordered breathing is now a well-established branch of the health business. Veale runs a purpose-built diagnostic laboratory near Auckland's Ascot Hospital, one of many in the country.
Auckland Hospital has four, Waikato and Wellington and Christchurch one each. And there are ambulatory services based in Tauranga, Palmerston North, Hawkes Bay and Gisborne with devices to test your sleep at home.
Veale's Auckland Respiratory and Sleep Institute began with two-bed facility in Mercy Hospital about 10 years ago. The new six-bed facility opened in April last year.
Patients spend the night sleeping under watch. They are wired with electrotrodes to their head, throat, chest, abdomen and legs. The wiring, plugged to a bedside machine, is extremely light and allows the sleeper to move easily.
A camera in the room allows technicians to keep a constant watch. The electrodes produce a night-long record of the patient's sleep phases, body positions, heart rate, blood oxygen level, snoring and incidents of apnoea and hypopnea (partial breathing obstruction).
At any time, Veale estimates there are probably between 3000 and 5000 Aucklanders receiving treatment for sleep disorders. His clinic sees 600 to 700 a year.
But the numbers seeking treatment are thought to be just a fraction of the problem. A 2009 study suggested about 9 per cent of women and 24 per cent of men in the general population have sleep-disordered breathing and a majority of those affected remain undiagnosed.
More than five obstructions an hour is abnormal, Veale says. "But we don't think there is a significant medical threat until there are over 30 per hour. Between five and 30, there are variable impacts on quality of life."
Besides daytime drowsiness, the person is likely to feel a loss of motivation, an inability to concentrate in meetings, have difficulty in making decisions and reduced libido.
People referred to him for treatment can be quite proud of their ability to snooze. When he asks if they sleep well, he often hears, "I can sleep anywhere, Doctor."
That is a danger sign. Another is, "at night I go out like a light - as soon as my head hits the pillow".
That is not "normal" either, he says. A normal, healthy night's sleep begins some time after going the bed, proceeds uninterrupted through several physiological phases and leaves you feeling rested, refreshed and alert for a full day.
Cost of sweet dreams
Sleep apnoea can be controlled but not cured.
Sleep clinics usually recommend a bedside machine connected to a device strapped to the sleeper's face, maintaining sufficient air pressure in the upper airway to keep it open.
Alternatively, there are oral and dental devices that are designed to hold the tongue or lower jaw forward, which help keep the airway open during sleep.
More drastically, there is surgery. One operation involves removing some of the soft palate at the back of the mouth, another takes tissue from the base of the tongue. Some people, says Veale, opt for full craniofacial surgery that brings their face forward or changes their jaw.
Trachiostomy - making an opening in the throat for breathing to bypass the obstruction - was the original remedy for serious apnoea and it is still done occasionally.
The more common removal of tonsils and adenoids is effective for children, he says, but adults who have had them removed may still need a breathing aid.
None of the surgical solutions are as effective as the air pressure device, he says, but at least the effect is permanent, whereas the device is effective only when it is used, "when it is always effective".
But it is expensive. District health boards may fund CPAP (Continuous Positive Airway Pressure) machines as well as sleep studies but priority is given to the most serious cases. Otherwise, a night's sleep study in a clinic will cost you $1350, or $450 for a sleep study in your home.
CPAP machines range from $1400-$1500 for a fixed pressure machine suitable for most patients, to $2500 for a variable pressure machine that some require.
Dental devices are a bit more expensive because they have to be fitted to the user.
Dozing behind the wheel
Should people with sleep apnoea be allowed to drive?
Medical studies suggest obstructive sleep apnoea increases the risk of motor accidents but the number of accidents attributed to it remains quite low.
Up to two-thirds of people being treated for it have never had a recorded crash.
In some countries all commercial drivers have to be assessed for sleep apnoea and treated if necessary.
Andrew Veale is "in two minds" on the merits of driving bans.
"On one hand, you have a lot of drivers who are sleepy but don't have sleep apnoea. And you have a lot of people with obstructive sleep apnoea who never nod off when they are driving.
"You have others who nod off when driving but have never had a crash because the nodding-off is so brief. A third group recognise they are sleepy [so] pull to the side.
"So to have a blanket rule that anyone with sleep apnoea shouldn't drive wouldn't be appropriate."
The other difficulty with a driving ban is that it would discourage apnoea sufferers from coming forward for treatment.
Veale points out that those who do come forward but refuse the treatment - which often involves wearing a device on your face every night - can have their driving licences cancelled on the report of a sleep physician.
"The people that I say shouldn't drive are those that have proven they are at risk by a previous crash or near crash. I try to get them treatment as fast as possible and advise them not to drive until it has been sorted."
He fears that if commercial drivers stood to lose their licence, they would be deterred from coming forward by the current waiting list for treatment.
"If we said to a truck driver we'd prefer you didn't drive and referred him to a publicly funded sleep study where he'd be seen in five months - that's the current waiting time - he won't tell you about it."
In Australia, he says, there is a suggestion that every truck driver should have a sleep study every year. He thinks that would be excessive.
Canadian sleep physician Charles George in a 2007 report suggested that the right to drive should cease at certain levels of sleep apnoea, just as it does for levels of alcohol in the blood.
But he acknowledged that apnoea could not be as accurately measured.
Education was the key to risk management, he concluded. "Not only must we continue to educate the public and industry about the dangers of drowsy driving, whatever the cause, but educate governments and insurance companies about the need to support the diagnosis and treatment of sleep apnoea."
Heart patients needed for study
Hundreds of New Zealand volunteers are wanted for a international sleep study. Researchers want at least 350 people with a history of coronary artery disease or strokes to investigate a new approach for treating sleep apnoea.
The study is trying to discover whether the use of sleeping masks, which direct air into the nose or mouth, can reduce the risk of heart failure or stroke in patients who suffer from apnoea.
People who qualify will get four years of free health checks. Five sites in New Zealand - Waikato, Tauranga and Hutt Hospitals, and respiratory research groups in Canterbury and Otago - are looking for volunteers.
Besides 350 New Zealanders, the study will include 5000 patients from China, Australia, Brazil and India. For details go to www.savetrial.org