Snoring is the act of breathing through the open mouth in such a way as to cause a vibration of the uvula and soft palate, thus giving rise to a sound which may vary from a soft noise to a loud unpleasant sound. This most commonly occurs during sleep.

The cause of snoring is having a blockage in the airway passage. When the airflow in the breathing passage becomes irregular due to the blockage, the soft palate will start vibrating. This vibrating of the soft palate is what causes the snoring sound.

Snoring is a problem if:

• you stop breathing during sleep and have to wake up to catch your breath,
• you are disturbing your sleep partner, or
• you are losing sleep because of your snoring.

In addition to problems stemming from sleep deprivation, snoring can cause more serious health problems. Snoring has been linked to increased risk of stroke; diabetes; high blood pressure; and heart disease. Snoring can also be a symptom of sleep apnea.

Numerical statistics on snoring are often contradictory, but at least 30% of the adult population and perhaps as many as 50% of people in some demographics snore. According to Dr. William C Dement, of the Stanford Sleep Center, anyone who snores and has daytime drowsiness should be evaluated for sleep disorders.

Sleep apnea is characterized by pauses in breathing during sleep. These episodes, called apneas (literally, "without breath"), each last long enough so one or more breaths are missed, and occur repeatedly throughout sleep. There are two distinct forms of sleep apnea: Central and Obstructive. Breathing is interrupted by the lack of effort in Central Sleep Apnea, but from a physical block to airflow despite effort in Obstructive Sleep Apnea.  Regardless of type, the individual affected with sleep apnea is rarely (if ever) aware of having difficulty breathing, even upon awakening. Sleep apnea is recognized as a problem by others witnessing the individual during episodes, or is suspected because of its effects on the body. The definitive diagnosis of sleep apnea is made by polysomnography.

In Central Sleep Apnea, the brain's control centers "forget" to breathe during sleep. The sleeper stops breathing, and then starts again. There is no effort made to breathe during the pause in breathing: there are no chest movements and no struggling, just stillness. After the episode of apnea, breathing may be faster for a period of time, a compensatory mechanism to blow off retained waste gasses and absorb more oxygen.

Obstructive Sleep Apnea is much more common than central sleep apnea. Approximately 1 in 5 American adults have some form of obstructive sleep apnea. Signs of obstructive sleep apnea can include loud snoring, morning headaches, trouble concentrating, irritability, daytime fatigue, mood or behavior changes, increased heart rate, anxiety, and depression, increased frequency of urination, bedwetting, esophageal reflux and heavy sweating at night.

Insomnia is characterized by an inability to fall sleep and/or remain asleep for a reasonable period. Insomniacs typically complain of being unable to close their eyes or "rest their mind" for more than a few minutes at a time. Both organic and nonorganic insomnia constitute a sleep disorder. It is often caused by fear, stress, anxiety, medications, herbs, caffeine or sometimes for no apparent reason. An overactive mind or physical pain may also be causes. Finding the underlying cause of insomnia is usually necessary to treat it.

According to the U.S. Department of Health and Human Services, approximately 60 million Americans suffer from insomnia each year. Insomnia tends to increase with age and affects about 40 percent of women and 30 percent of men. The average American gets 7 hours of sleep, instead of the 8 to 10 hours recommended by doctors.

Narcolepsy is a neurological condition characterized by Excessive Daytime Sleepiness (EDS) and unintended episodes of sleep.

The main characteristic of narcolepsy is overwhelming excessive daytime sleepiness, even after adequate nighttime sleep. A person with narcolepsy is likely to become drowsy or to fall asleep, often at inappropriate times and places. Daytime naps may occur with or without warning and may be irresistible. These naps can occur several times a day. They are typically refreshing, but only for a few hours. Drowsiness may persist for prolonged periods of time. In addition, night-time sleep may be fragmented with frequent wakenings.

Four other classic symptoms of narcolepsy, which may not occur in all patients, are:

• Cataplexy: sudden episodes of loss of muscle function, ranging from slight weakness (such as limpness at the neck or knees, sagging facial muscles, or inability to speak clearly) to complete body collapse. Episodes may be triggered by sudden emotional reactions such as laughter, anger, surprise, or fear, and may last from a few seconds to several minutes. The person remains conscious throughout the episode.
• Sleep paralysis: temporary inability to talk or move when waking up. It may last a few seconds to minutes. Often frightening but not dangerous.
• Hypnagogic hallucinations: vivid, often frightening, dream-like experiences that occur while dozing, falling asleep and/or while awakening.
• Automatic behavior: Automatic behavior occurs when a person continues to function (talking, putting things away, etc.) during sleep episodes, but awakens with no memory of performing such activities. It is estimated that up to 40 percent of people with narcolepsy experience automatic behavior during sleep episodes.

It is estimated that there are as many as 3 million people worldwide affected by narcolepsy. In the United States it is estimated that narcolepsy afflicts as many as 200,000 Americans, but fewer than 50,000 are diagnosed. It is as widespread as Parkinson's disease or multiple sclerosis. Narcolepsy is often mistaken for depression, epilepsy, or the side effects of medications.

Restless legs syndrome is a neurological disorder that is poorly understood.

RLS may be described as uncontrollable urges to move the limbs in order to stop uncomfortable, painful or odd sensations in the body, most commonly in the legs. Moving the affected body part reduces the sensations, providing temporary relief. The sensations and need to move may return immediately after ceasing movement, or at a later time. RLS may start at any age, including early childhood, and is a progressive disease for a certain portion of those afflicted.  It often results in a lifelong insomnia unless properly treated.

In 2003 National Institutes of Health (NIH) defined RLS to include the following:

1. an urge to move the limbs with or without sensations
2. worsening at rest
3. improvement with activity
4. worsening in the evening or night.

About 10 percent of adults in North America and Europe may experience RLS symptoms, according to the National Sleep Foundation.

Often sufferers think they are the only ones to be afflicted by this peculiar condition and are relieved when they find out that many others also suffer from it. The severity and frequency of the disorder vary tremendously. Many people only experience symptoms when they try to sleep, while other experience symptoms during the day. It is common to have symptoms on long car rides or during any long period of inactivity (like watching television or a movie, attending a musical or theatrical performance, etc.) Approximately 80-90% of people with RLS also have PLMD, Periodic Limb Movement Disorder, which causes slow "jerks" or flexions of the affected body part.

Periodic Limb Movement Disorder (PLMD) is a sleep disorder where the patient moves involuntarily during sleep. It can range from a small movement in the ankles and toes to wild flailing of all four limbs. These movements, which are more common in the legs than arms, occur for between 0.5 and 10 seconds, recurring at intervals of 5 to 90 seconds. A formal diagnosis of PLMD requires documentation of these movements observed on a polysomnogram.

PLMD is a cause of insomnia and daytime sleepiness. The incidence of this disorder increases with age. It is estimated to occur in 5% of people age 30 to 50 and in 44% of people over the age of 65. As many as 12.2% of patients suffering from insomnia and 3.5% of patients suffering from excessive daytime sleepiness may experience PLMD.

Rapid Eye Movement Behavior Disorder or RBD was first described in 1986. The major feature of RBD is loss of muscle atonia (paralysis) during otherwise intact REM sleep (the stage of sleep in which most vivid dreaming occurs). This loss of motor inhibition leads to a wide spectrum of behavioral release during sleep. This extends from simple limb twitches to more complex integrated movements where sufferers appear to be unconsciously acting out their dreams. These behaviors are often violent in nature and commonly result in injury to either the patient or their bed partner. Injuries range from bruises and cuts to fractures and other serious injuries. In contrast, all other aspects of sleep appear similar to normal.

The estimated prevalence of RBD is around 0.5% in individuals aged 15-100. It is far more common in males: most studies report that only around a tenth of sufferers are female. The mean age of onset is estimated to be around 60 years of age.

Various conditions are very similar to RBD in that sufferers exhibit excessive sleep movement and potentially violent behavior. Such disorders include sleepwalking and sleep terrors, which are associated with other stages of sleep, nocturnal seizures and obstructive sleep apnea which can induce arousals from REM sleep associated with complex behaviors. Because of the similarities between the conditions, polysomnography plays an important role in confirming RBD diagnosis.