Up to 70 million Americans have a sleep disorder such as chronic insomnia—and this condition and others can bring persistent difficulty sleeping and subsequent trouble functioning during the day. More than 40 million don’t get properly diagnosed or treated, according to research published in the journal Sleep Medicine.

Some people may be unaware of sleep interruptions, and often, “patients don’t bring their sleep to the attention of doctors because they don’t think it’s ‘medical’ or think they should tough it out,” says Matt T. Bianchi, M.D., Ph.D., director of the sleep division at Massachusetts General Hospital in Boston.

Past surveys have shown that medical schools have formally devoted, on average, less than 2 hours to sleep medicine, and doctors might not routinely discuss sleep problems at office visits. A study in the Journal of Clinical Sleep Medicine found that only 25 percent of primary care providers asked new patients about insomnia or other sleep issues, although many had signs of problems. Doctors might also find it hard to pinpoint which of the 60 sleep disorders is the culprit because symptoms may be unclear, and other illnesses and habits may affect rest.

If you often have trouble falling or staying asleep, or can’t function normally, your primary care provider can help rule out illnesses that can affect sleep, such as depression and overactive thyroid, and might be able to zero in on the cause of your sleep problem. If not, a board-certified sleep specialist can conduct a detailed evaluation. Here we cover how three common sleep disorders are evaluated.

Read our special report on why Americans can't sleep, which includes information on how to fall asleep the natural way, details on the problem with sleeping pills, and much more.

Chronic Insomnia

Affecting about 10 to 15 percent of adults, chronic insomnia is defined as trouble falling or staying asleep at least three times per week for three months or longer (Typical insomnia occurs less often or for a shorter period of time). If you are experiencing these sleep problems, your doctor will ask about symptoms and their effects—whether, for example, your partner says that you snore. He will also ask lifestyle questions and try to identify whether habits such as heavy caffeine or alcohol consumption, use of electronic devices close to bedtime, or medications could be contributing.

If your doctor can’t get to the root of your insomnia, see a sleep medicine physician. This specialist might have you keep a sleep, exercise, and food and alcohol diary, and might order actigraphy testing, which helps track your sleep schedule with a wristwatchlike device. If the sleep medicine physician suspects another sleep-disrupting problem, he can order an overnight sleep lab polysomnogram. Here, as you sleep, electrodes record your brain waves, heartbeat, breathing, eye movements and blood oxygen levels. Sensors measure chest movement and the strength and duration of your breaths.

People who can't sleep might suffer from chronic insomnia

Obstructive Sleep Apnea

Obstructive sleep apnea, or OSA, characterized by numerous brief pauses in breathing during sleep, can cause significant daytime sleepiness. Sufferers may also fall asleep at inappropriate times.

An estimated 25 million Americans have OSA, with 12 million to 18 million undiagnosed. And research published in the Journal of Clinical Sleep Medicine suggests that OSA may often be misdiagnosed as depression.

To properly diagnose OSA, you’ll need a sleep lab polysomnogram or an overnight home sleep apnea test, where electrodes record breathing and heart rate, blood ­oxygen levels, and chest movements but usually not brain waves. This may not detect mild apnea and is prone to false negatives, so if results are negative but your doctor strongly suspects apnea, you’ll need a polysomnogram.

Restless Legs Syndrome

Restless legs syndrome, or RLS, which affects about 10 percent of American adults, causes leg sensations such as burning, a creepy-crawly feeling, throbbing, and an uncontrollable urge to move your lower limbs. That can make it hard to fall asleep and can wake you up.

Doctors might mistake RLS for conditions such as anxiety, arthritis, back injury, and poor circulation. It can also mimic diabetic neuropathy. In one study, 81 percent of people with RLS reported symptoms to their doctor, but just 6 percent received proper diagnoses.

You don’t need a polysomnogram to diagnose RLS unless your doctor can’t pinpoint which sleep disorder you have. A symptom history and exam should be enough, says the American Academy of Sleep Medicine.

Editor's Note: This article also appeared in the March 2016 issue of Consumer Reports on Health.