I got the kind of neck brace normally used by health care practitioners for immobilizing a person's head and wore it on several long haul flights during the year, lashed to the headrest on the seat back with an improvised system of belts, along with a blindfold. It enabled restful sleep during the flights with the only downside being that I looked weird. Normal travel pillows are useless to me because the tendency for my head is to hang forward when I'm on a plane.