 Obstructive sleep apnea OSA is common and has major health implications but treatment options are limited. Interestingly, the severity of OSA is profoundly reduced in deep sleep called slow wave sleep, potentially via an increase in the stimulus required to arouse from sleep. Here the investigators test the idea that the medication called tiagabine improves slow wave sleep and reduces OSA severity. The investigators will also test whether tiagabine raises the arousal threshold more negative esophageal pressure, and whether detailed OSA phenotyping characteristics can predict the improvement in OSA severity with this intervention. 