http://www.nhlbi.nih.gov/health/dci/Diseases/SleepApnea/SleepApnea_WhatIs.html
National Heart, Lung, and Blood Institute, National Institutes of Health
This publication discusses sleep apnea, a common disorder in which you have one or more pauses in breathing or shallow breaths while you sleep. It usually is a chronic (ongoing) condition that disrupts your sleep 3 or more nights each week. This results in poor sleep quality that makes you tired during the day.