This research study will take place in conjunction with normal clinical practice. Patients with depression and sleep disorders are commonly seen in our sleep clinic and mirtazapine is one of several antidepressants that is prescribed by our clinicians. In this study, we will follow a group of patients who have been prescribed mirtazapine by one of our clinic physicians and who meet the inclusion and exclusion listed below. There will be an additional number of sleep studies (10 total versus the usual 2 or 3) performed; the usual daytime testing will be conducted as part of the standard of care (Multiple Sleep Latency Test (MSLT) and Maintenance of Wakefulness Test (MWT)); we will administer additional questionnaires to assess subjective sleepiness, alertness and fatigue; and, driving simulator testing will be conducted in accordance with our normal standard of care.