People with obstructive sleep apnea (OSA) have disrupted sleep and low blood oxygen levels. When obstructive sleep apnea occurs, the tongue is sucked against the back of the throat. This blocks the upper airway and airflow stops. When the oxygen level in the brain becomes low enough, the sleeper partially awakens, the obstruction in the throat clears, and the flow of air starts again, usually with a loud gasp.
Repeated cycles of decreased oxygenation lead to very serious cardiovascular problems. Additionally, these individuals suffer from excessive daytime sleepiness, depression, and loss of concentration.
Some patients have obstructions that are less severe called Upper Airway Resistance Syndrome (UARS). In either case, the individuals suffer many of the same symptoms.