The purpose of this study is to determine if obstructive sleep apnea (OSA)—a condition in which respiration and oxygenation are affected during sleep—can cause abnormal autonomic function and blood sugar (glucose) processing, which could lead to diabetes, or pre-diabetic conditions. The autonomic system controls heart rate, blood pressure, breathing, and other functions of the body. OSA and diabetes are commonly found in overweight individuals and both can cause increased risk of heart disease and strokes. OSA can be treated using nasal continuous positive airway pressure (CPAP) which overcomes the obstruction to airflow that occurs in OSA.