People with hypopnea due to airflow obstruction often have loud, heavy snoring that is interrupted with choking sounds or loud snorts followed by periods of silence, because not enough air can flow into the lungs through the mouth and nose. The periods of silence can last 20 seconds or longer and can happen many times each hour, resulting in poor sleep and reduced levels of oxygen in the blood. Other symptoms of hypopnea may include depression, forgetfulness, mood or behaviour changes, trouble concentrating, loss of energy, nervousness, and morning headaches. Not all people with hypopnea experience all of these symptoms and not everyone who has these symptoms has hypopnea. Consequences
Hypopnea is a disorder that may result in excessive daytime sleepiness and compromised quality of life, including traffic accidents, diminished productivity in the workplace, and emotional problems. Cardiovascular consequences of hypopnea may include myocardial infarction, hypertension, coronary heart disease as well other problems such as stroke, psychiatric problems, impotence, cognitive dysfunction and memory loss.
Causes
Among the causes of hypopnea are:

anatomical defects such as nasal septum deformation or congenital narrowness of nasal meatus and the gullet
acute tonsillitis and/or adenoiditis
obesity or being overweight
neuromuscular disease or any condition that entails weakened respiratory muscles
hypoventilation syndromes involving compromised or failed respiratory drive
use of sedatives, for example sleeping pills
hazardous alcohol use
smoking
aging
others, most of which are also typical causes of airway obstruction, snoring and sleep apnea

Diagnosis
In the context of diagnosis and treatment of sleep disorders, a hypopnea is not considered to be clinically significant unless there is a 30% or greater reduction in flow lasting for 10 seconds or longer and an associated 4% or greater desaturation in the persons O2 levels, or if it results in arousal or fragmentation of sleep. The direct consequence of hypopnea (as well as apnea) is that the CO2 in the blood increases and the oxygen level in the patients blood decrease is proportionate to the severity of the airway obstruction. This disruptive pattern of breathing generates disruptive sleep patterns, the consequences of which being that those individuals may exhibit increased fatigability, lethargy, decreased ability to concentrate, increased irritability, and morning headaches. Basically, those individuals are extremely tired due to their inability to get a good nights sleep. Hypopneas can be either central i.e., as part of a waxing and waning in breathing effort, or obstructive in origin. During an obstructive hypopnea, in comparison to an obstructive apnea, the airway is only partially closed.