Melatonin's Effect on Nighttime Blood Pressure and Sleep in OSA Patients (MEBP-OSA)

The goal of this clinical trial is to learn if melatonin works to treat comorbid insomnia in adults with OSA and nocturnal non-dipping blood pressure pattern. The main question it aims to answer is: Does melatonin maintain sleep during night and recover the dipping blood pressure pattern? Participants will: - Take melatonin or the habitual treatment every day for one month - Visit the clinic 11 times for one month - Keep a diary of their symptom and activities and use twice a 24 h ambulatory blood pressure monitoring (ABPM), attend two overnight polysomnography studies, and use an actigraph every day for 2 weeks. Researchers will compare melatonin to the habitual treatment to see if melatonin works to treat insomnia and recover the dipping blood pressure pattern. The medical problems that participants would have when taking melatonin are: - changes in blood pressure and cholesterol - Increased risk of contracting immune system disorders - Possible increased risk of liver damage.