In OSA, the patient stops breathing many times while he sleeps.

Dr Ignatius Mark, an ear, nose and throat surgeon at Ascent Ear Nose Throat Specialist Group, said that this is caused by a blockage in several sites in the upper airways (made up of the nose, mouth and throat), making it hard for air to enter the lungs.

OSA patients snore loudly and often choke but are unaware that they are doing so, he said. The frequent sleep disruption is due to the drop in oxygen levels, which “wakes” the brain up repeatedly to open the airways.

Some patients wake up tired and then suffer from excessive daytime sleepiness. They may fall asleep very easily, which is especially dangerous when they are driving or operating heavy machinery, said Dr Mark.

Their risk of high blood pressure, heart disease and stroke also increases, due to the lack of oxygen and frequent choking, he added.

Being overweight, having small jaw bones, throat lumps and having airways that easily collapse, increase one’s risk of getting the condition.

OSA is diagnosed by an overnight polysomnogram or sleep test.

Patients are individually treated, said Dr Mark. The first step usually involves lifestyle changes, like losing excess weight and quitting smoking.

More severe cases may require positive airway pressure therapy. This involves the use of a mask, connected to an air pressure delivery device. Worn during sleep, it keeps the upper airways open and prevents choking and disruptions in breathing.

Surgery is considered only under three scenarios: when there is a simple type of obstruction in the airways, for example, large tonsils; failure of non-surgical treatment; or when nasal obstruction, like a blocked nose, interferes with non-surgical treatment, said Dr Mark.

Another cause of hypersomnia is narcolepsy, a neurological disorder that causes sufferers to suddenly fall asleep during the day, even when they are talking or driving.

This condition affects only about 0.05 per cent of the population in Singapore and mostly among males and adolescents.

Its cause is unknown, but genetics, head trauma and autoimmune responses may trigger the disorder.

The body’s immune system may play a role in destroying hypocretin, a hormone that promotes wakefulness. People with narcolepsy have a deficiency of this hormone, explaining their daytime sleepiness.

Dr K. Puvanendran, the founding director of the sleep disorder unit at Singapore General Hospital, said that these sleep attacks are usually brief lasting just a few seconds, but some can last as long as 10 to 20 minutes each. Patients usually wake up feeling refreshed.

Brief attacks may lead to car accidents, say, when the patient is driving, he said.

The normal process of falling asleep starts off with stages of light, then deep sleep. After about 90 minutes, rapid eye movement (REM) sleep occurs. It is in REM sleep that dreams and temporary paralysis, which prevents dreams from being acted out, occur.

Narcoleptics, however, suddenly fall into REM sleep without first going through the prior stages of sleep. Hence, they often fall asleep experiencing hypnogogic hallucinations, which are odd dreams that seem real, and brief episodes of paralysis when they wake, said Dr Puvanendran.

For example, a narcoleptic experiencing a hypnogogic hallucination may “sense” someone touching him.

When the phone rings while the narcoleptic is asleep, he hears it and wakes up but cannot move to pick up the phone, he explained.

Another symptom is cataplexy, or sudden muscle weakness, often triggered by laughter or fear. A person
with narcolepsy may be laughing at a joke and suddenly finds himself unable to move.

Narcolepsy is diagnosed through overnight and day sleep tests. The condition is lifelong but can be managed successfully through medication, like brain stimulants.

Taking power naps during the day also helps, said Dr Puvanendran.

Excessive day sleeping can also be a symptom of depression.

Dr Bernadine Woo, a consultant psychiatrist at the child and adolescent psychiatry department at the Institute of Mental Health, said that depressed people may sleep too much because they want to avoid dealing with their problems.

They may also have lost interest in doing things they used to enjoy, she added.

Other depression symptoms, like low moods, irritability and guilt usually accompany oversleeping. Dr Woo said such sleeping habits usually improve when the depression is treated, usually with medication, psychotherapy or a combination of both.

If you suspect that you have an oversleeping disorder, ask yourself this question: Do you sleep fewer than five or six hours a day routinely? If the answer is yes, you may simply be tired because of lack of sleep, said Dr Lim Li Ling, a consultant neurologist at the Singapore Neurology & Sleep Centre and president of the Singapore Sleep Society.

However, persistent and unexplained sleepiness, despite having at least six to eight hours of sleep daily, may indicate the presence of an underlying sleep disorder and a visit to a doctor is recommended, she said.