Exclusion Criteria: respiratory distress; COPD requiring oxygen; primary intracranial hemorrhage on admission brain imaging; time from symptom onset to sleep study or CPAP treatment >72 hours or time from hospital admission to sleep study or CPAP treatment >48 hours; life expectancy less than 6 months; inability to provide informed consent; inability to communicate in English; residence outside the greater New Haven area; or any condition where the monitoring required by the study would constitute a risk to the patient or impair his or her care.