At first, Imelda assumed it was stress causing her sleep disturbance -- a fitful sleep, weird dreams and morning headaches. But she became concerned when it continued even when she had nothing to worry about.

"I have enough sleep, like six to seven hours. But often it's not a good sleep. I have tiring dreams, like running or climbing things, and I often choke during sleep. The next morning, I feel tired and irritated instead of feeling fresh," said the 26-year-old journalist.

She also snores, a problem since childhood which she attributed to her asthma.

The problem has continued for three months now, despite various efforts -- aromatherapy, supplement pills, cutting down on caffeine -- to obtain a satisfactory sleep.

Though it has yet to be medically diagnosed, Imelda's symptoms show she may be suffering from Obstructive Sleep Apnea (OSA). In the long run, OSA can be lethal as it can lead to hypertension, stroke and even heart attack.

"OSA is often called a silent killer because patients can undergo sudden death when they are asleep. Yes, it is that dangerous, but people are not aware of it," said pulmonologist Janto Gunawan Lingga from the Sleep Disorder Clinic at Mitra Kemayoran Hospital, Central Jakarta.

OSA involves recurrent episodes during sleep, when a person's throat closes and they cannot suck air into their lungs (apnea).

It occurs because the muscles that normally hold the throat open when people are awake relax during sleep and allow it to narrow.

The partially closed throat and relaxed muscles block the passage of air, episodes which can last up to two minutes.

Episodes continue throughout sleep, and only cease upon awakening, when the muscles strengthen again.

"So, it looks like one is breathing, but there's no air passing through the throat. This cycle may be repeated hundreds of times a night while the sufferer doesn't realize it's happening," Janto said.

"The OSA episodes can cause the reduction of the oxygen level in the blood. The accumulated process of it will disturb the system, especially the nerve system, and can lead to stroke, cardiac arrest during sleep, hypertension, heart attack, reduced sex drive and impotence."

Cardinal symptoms of OSA sufferers are fatigue and tiredness during the day, and excessive daytime sleepiness. Loud snoring is another symptom -- especially if it is repeatedly punctuated by brief periods of silence or choking sounds.

Others include restless sleep and repeated struggling to breath, mood swings and irritability, as well as snorting, gasping and choking during sleep. Predisposing factors include obesity, a small jaw and thick neck.

"There are other symptoms reported but not common, like insomnia, difficulty in concentrating, forgetfulness and frequent nocturnal urination or nocturia," Janto said.

In young children, large tonsils and adenoids contribute to the incidence of OSA.

According to Janto, sleep apnea is tied to anatomical factors -- such as a thick soft palate and thick neck -- but is not related to external factors like nutrition.

"Overweight people, however, have a higher risk," he said.

Aside from the aforementioned health risks, there is also a constant risk of serious accidents from impaired functions, such as falling asleep at the wheel or poor performance at work, and the affect on personal relationships.

In the United States, OSA has raised concerns because around 30 million Americans suffer from it. Many millions more are predisposed to it because of factors like obesity.

An adult male has 50/50 odds that his breathing is not normal when he is asleep.

The Sleep Disorder Clinic here does not have statistics on the prevalence of OSA in this country, but it has treated about 50 people since its opening in 2001.

"The problem is low awareness. So far, people come here when the problem is already bad. Nobody takes snoring seriously, while it can be a symptom of illness," Janto said.

Often, as occurred in the U.S., even physicians are not knowledgeable about the ailment.

If you suspect you have OSA, first try to change your sleeping position so that you sleep on your side.

"That way, the muscle is less relaxed and the air path is enlarged. Put something on your back to hold the position, like sewing a tennis ball to your clothes. The tennis ball way is proven effective," Janto said.

Diet and exercise also helps for overweight patients.

For advanced cases, help should be sought from a physician to undergo a diagnostic sleep study with a polysomnogram. The device can monitor air flow, respiratory effort, blood oxygen level, snoring, body position, brain waves, eye movements and muscle activity.

The most common treatment is using a machine called continuous positive airway pressure (CPAP), which delivers air pressure through a small nasal mask that the patient wears while sleeping. The machine is expensive, costing at least Rp 8 million (US$1,000).

OSA can also be treated surgically, but costs and success rates may vary greatly.

"Sometimes it causes a bit of fluid to come out of your nose when you drink. Many patients also refuse to have dental surgery, to move the jaw forward," Janto said.