Not sure about the pressure messing up the dose of morphine but...

Norco is hydrocodone. Bloody strong opiate. Highly emetogenic at the best of times.

The air you’re breathing on the plane is at a lower pressure which reduces the amount of oxygen in your blood. Opiates cause respiratory depression which will only accentuate this effect.

Added to the fact that you’ll be relatively more dehydrated (because of the lower cabin humidity, amongst other things), it strikes me as a bad idea all round to be taking this to help you sleep

If you need help with getting sleep on planes, the best plan is to see your doctor for something appropriate

edit: typo on drug generic