Sleep apnea (or "sleep apnoea" in British english, common misspellings — sleep apnia, sleep apena and sleep aponea) can be a very serious sleep disorder and could be fatal if untreated. See also: Can Sleep Apnea Cause Death?
Basically, sleep apnea is an interruption to breathing during sleep. There are three main types of sleep apnea that affect breathing in different ways.
Central sleep apnea occurs when there is insufficent respiratory effort and breathing stops intermittently throughout the night. This is due to the signals from the brain that tell the body to breathe are not sent when they should be. This is a problem that originates with the central nervous system and can come about as a result of brain injury, virus, tumor or other factors that affect the brain as well as chronic respiratory disease.
The second type is obstructive sleep apnea. This is because there is an actual physical obstruction that prevents a proper breathing pattern. This form of the sleep disorder is most common among overweight individuals. Other causes for obstruction to the airway include enlarged tonsils or adenoids, deviated septum, enlarged tongue and relaxed muscles in the neck (which can be caused or exacerbated by alcohol or sedatives).
Complex sleep apnea refers to a combination of central and obstructive conditions that cause the apnea episodes.
Each of these interruptions (or apnea) can result in one or more breaths being missed and may go unnoticed and undiagnosed for years.
Often a problem is only found out by the symptoms caused by the lack of restful sleep such as daytime tiredness and fatigue. In some cases the apnea is noticed by a spouse or family member. See Symptoms of Sleep Apnea.
Fortunately, some progress has been made in treating these conditions from the mild to the severe.
In mild cases simply sleeping on your side can help. There are specially shaped pillows and shirts that are designed to promote sleeping in this position. There are also oral appliances that can be custom fitted by a dentist that can help by causing the lower jaw to project forward slightly and opening the airway.
In more severe cases of this sleep disorder CPAP machines are available. CPAP stands for Continuous Positive Airway Pressure. CPAP helps to maintain airflow through assisting inhalation. (In some cases a BiPAP machine may be required with provides assistance for both inhaling and exhaling.)
Surgery is an option in the case of obstructive apnea. There are various approaches depending on the particular case of each sleep apnea sufferer.
Whichever form of sleep apnea, it can be difficult to get a diagnosis without having a "sleep test" or "sleep study" done. These are generally done overnight and will monitor the electical activity of your brain with a EEG (Electroencephalograph) as well as the oxygen saturation levels of your blood.
If you have been fatigued for a long time and don't feel rested after a night's sleep see your doctor and ask about being checked for sleep apnea, especially if you are overweight.