In the last installment of the four-part series "The Science of Sleep," doctors try to treat sleep apnea, which not only causes snoring but can also lead to more serious health conditions. NY1's Kafi Drexel filed the following report.

For Charmaine Hescott, trying to get to sleep at night is literally a nightmare.

"I'm just looking up at the ceiling saying, 'What did I do?, Did I do something wrong? Am I being haunted?'" she says.

Lack of sleep is definitely taking its toll on the 39-year-old.

"I am looking older than my age and, you know, I seem to put on a lot of weight," says Hescott.

Jorge Gomez, a 42-year-old former World Trade clean-up worker, also has trouble with sleep.

"Wake up sometimes two, three times during the night. My wife says I've been snoring since about a year ago, two years ago," says Gomez.

Doctors say Hescott and Gomez are likely candidates for obstructive sleep apnea, a condition that affects more than 18 million adults across the country. So Hescott participates in a sleep study at Montefiore Medical Center in Norwood, Bronx, while Gomez takes part of a study at Mount Sinai Comprehensive Center for Sleep Medicine on the Upper East Side.

"In obstructive sleep apnea, what happens is we fall asleep and all our muscles relax. The muscles keeping our windpipe open also relax. Those muscles lose their tone and the wind pipe starts closing and collapsing," says Dr. Jorge Mallea of Mt. Sinai.

That condition causes snoring, or frequent waking at night, because of an alarm system that triggers in the body when it is not getting enough oxygen.

In the sleep studies, the patients are hooked up to leads, and infrared cameras record how they sleep. Doctors and technicians monitor the patients' overnight brain activity on computer screens and keep track of air flow, the stages of the patients' sleep and other things.

If left untreated, apnea can lead to or worsen heart disease and other serious conditions. More than half of apnea patients are overweight or obese, and Hescott's doctors say her weight gain could be the result of her apnea.

"It's been shown that patients who don't sleep enough end up overweight for multiple reasons. Hormones that are produced while you are sleeping are important for losing and maintaining your weight," says Dr. Renee Monderer of Montefiore Medical Center.

After being diagnosed with apnea, Charles Hack, 62, was instructed to lose weight and was fitted with a special continuous positive airway pressure mask. While it is not the most comfortable fix, Hack says the CPAP breathing device is helping.

"My wife basically would complain to me that I would be getting up in the middle of the night. Apparently I don't get too many more complaints about snoring anymore," says Hack.

Sleep experts have been investigating ways to treat apnea, like special mouthguards and more advanced approaches to surgery.

Continuous patterns of not getting enough sleep are serious. If you have been suffering difficulty breathing, insomnia or other sleep-related problems for longer than a period of a few weeks, do not ignore it. See a doctor or a sleep specialist.