Obstructive sleep apnea (OSA) is a serious sleep disorder in which a person repeatedly stops breathing, or experiences shallow breathing for short periods of time during sleep. Daytime sleepiness is a common symptom of OSA and may affect an individual's level of alertness throughout the day. The primary purpose of this study is to evaluate the relationship between the severity of sleep-disordered breathing and levels of daytime alertness at baseline (untreated state) in a group of subjects with and without sleep apnea. In addition the change in daytime sleepiness in subjects with sleep apnea being treated with a continuous positive airway pressure (CPAP) machine, a common treatment for OSA will also be assessed.