A cpap machine causes a lot of air eating and hence there can be gas in the abdomean and bloating
This can give u a bad feeling of pain and discomfort. What u should do is that after u have used your machine breathe through your mouth out as much as u can for 5-10 breaths and try to remove the air.
You can also use a tablet of domperidone
10 mg daily in the morning to increase the activity of the abdomen and expulsion of the gas