More and more airlines are pulling their pillows from their flights. Good riddance! In addition to the questions of hygiene and sanitation, those pillows were largely useless. Do yourself and your neck a favor and upgrade.
As a licensed chiropractor, I see many patients who return from traveling with all sorts of new ailments and re-injured old ones. Usually, the injury occurs during the flight, due to long periods of sitting uncomfortably. The right travel pillow will not only allow you to relax, which offers its own health benefits, but help prevent soreness or even injury.
During the day, the postural muscles in your neck are in contraction, to support your head. When you relax, your neck muscles relax with you.
When you are lying in bed, gravity helps keep your head and body aligned. When you are sitting upright, like in an airplane chair, gravity is working against you. Especially, if you are trying to relax.