Sleep Apnea What Is Obstructive Sleep Apnea (OSA)? What Causes Obstructive Sleep Apnea? What Causes Central Sleep Apnea? What Are the Warning Signs of Sleep Apnea? When to See A Doctor? What are Sleep Studies? How Is Sleep Apnea Diagnosed? How is Sleep Apnea Treated? What Happens If Sleep Apnea Is Left Untreated?