The causes of sleep apnea vary between patients. Targeted therapy according to the underlying causes of sleep apnea in individual patients is likely to be most effective. However, current therapeutic options for sleep apnea are quite limited. The purpose of this physiological research study is to determine if taking eszopiclone (Lunesta)changes the breathing effort required to briefly wake people with obstructive sleep apnea from sleep (the arousal threshold) and if administration of the sedative medication eszopiclone (Lunesta) to certain sleep apnea patients (those with a low arousal threshold ie wake up easily) would be beneficial.