When obstructive sleep apnea occurs, the tongue is sucked against the back of the throat. This blocks the upper airway and air flow 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. People with obstructive sleep apnea (OSA) have disrupted sleep and low blood oxygen levels. OSA has been associated with cardiovascular problems and excessive daytime sleepiness. The condition known as upper airway resistance syndrome (UARS) lies midway between benign snoring and true obstructive sleep apnea. People with UARS suffer many of the symptoms of OSA but normal sleep testing will be negative.