An overnight diagnostic sleep study is used to definitively diagnose sleep apnea. A sleep study is also necessary in order to provide documentation to a health insurance company of a medical condition that requires treatment. This study is painless, non-invasive, and measures a number of physiological changes while you sleep. A medical device records the number of sleep disordered breathing events that occur during the night. The total number of events, known as "apneas" and/or "hypopneas", determines the severity of the apnea.