Simply put, melatonin makes you feel as if you're ready to sleep. And unlike traditional sleeping pills, you wake feeling refreshed, not hungover. If you're crossing time zones, melatonin can also ease jet lag. Melatonin's side effects are minimal, but the FDA has not approved it. It conforms to the shape of your face, but it isn't so tight that you can't blink.
Darkness triggers the hormones that bring on sleep.
The only downside to an eye mask is that it may not help much if the rest of the cabin is full of noisy activity.