Individuals with sleep apnea with and without glucose abnormalities will be age and BMI matched, and will undergo further autonomic and peripheral nerve testing. Individuals without diabetes will be followed for one year of CPAP treatment for their sleep apnea—with visits at 3 month intervals to evaluate glucose and autonomic function. Individuals without sleep apnea or diabetes will also undergo autonomic and peripheral nerve testing. Participants will also complete questionnaires to assess their sleepiness and symptoms of autonomic function.