Sleep apnea

Sleep apnea (or Sleep apnoea) is a problem certain people have: When they sleep, they may stop breathing for short periods. These periods can last for 10 seconds or more. 3-4 breaths are "missed". As a result of this, those affected are often tired during the day. Mainly because such people also tend to have microsleep, they should not drive vehicles. Sleep apnea is a treatable disease. 
Sleep apnea occurs when the muscles in the back of the throat relax too much to allow normal breathing. These muscles support structures including the back of the roof of the mouth (soft palate), the triangular piece of tissue hanging from the soft palate (uvula), the tonsils, and the tongue.
When the muscles relax, the airway narrows or closes when breathe in, hampering the breathing for 10 seconds or longer. This can lower the level of oxygen in the blood and cause a buildup of carbon dioxide.
Finding out if someone has sleep apnea.
People can ask their partner or family member if they are breathing strangely when they are sleeping.
Complication.
Diseases which may complicate sleep apnea are: obesity, high blood pressure, hyperlipidaemia, arrhythmia, polyemia, ischemic heart disease, cerebrovascular disease, diabetes etc.
Sleep apnea is a risk factor of arteriosclerotic disease.
Effects.
When there are no house mates, it may take time to discover this condition. When especially subjective symptoms are weak, the state will get worse gradually and it will start a serious problem.