Obstructive sleep apnea (OSA) has traditionally been attributed only to a collapsible upper airway. However, it is increasingly recognized that multiple additional non-anatomical mechanisms contribute to the disease. Higher rates of OSA in patients with post-traumatic stress disorder (PTSD) than in those without PTSD have been reported however the mechanism behind this increased prevalence has not been investigated. Our hypothesis is that patients with PTSD have a predisposition to OSA due to a lower respiratory arousal threshold (wake up too easily) than patients without PTSD. The goal of this project will be to study and compare the ArTH in patients with PTSD and those without. In addition, we plan to see whether medications can be used to increase the arousal threshold and treat OSA in patients with PTSD.