I found this in http://www.sleepapnea.org/resources/pubs/wrong.html
"It may help to take either Benedryl or Tylenol PM an hour before bedtime so that you are drowsy going to bed and so that it is less likely that you will awaken at night"
From what I understand, any muscle relaxant(that includes sleeping pills) makes apnea worse. Aren't cough syrups muscle relaxants?

