Obstructive Sleep Apnea, also known as OSA, is the partial or complete collapse of the upper airway or throat causing pauses in breathing (apneas). These blockages of upper airway can be caused by excessive or drooping of soft tissues, e.g. tongue, soft palate, uvula, or simply enlarged tonsils.
The pauses in breathing can drop down the oxygen level, which alerts the brain to lighten the stage of sleep and disrupt the sleep.