Before you look too hard for a way to sleep on long flights, check out
www.airhealth.org

I too am tall (6ft 4in) and ten years ago (age 55 then) was stuffed
into a 747 center section steerage seat for a rushed
Chicago-Tokyo-Chicago business trip. A few days after returning,
while bending over, I had a TIA (small stroke) that completely
paralyzed me on the right side for about an hour. A blood clot
apparently crossed over in my heart & went to my brain. I now know I
have a common (35 percent of us do) heart defect called a Patent
Foramen Ovale (PFO) that allows some blood to occasionally skip going
thru the lungs, which would otherwise have filtered the clot out.

It has been a dog fight with the FAA to renew my 3rd class medical
ever since.

Clot formation on long flights is well described on the referenced web
site. Briefly you want to keep hydrated and keep moving around.
Don't sleep for any length or you may generate a clot. If you are
lucky, it will only be like Dan Quayle's of about the same time, and
be caught by your lung, which also requires hospitalization. He was
in first class, yet it still happened to him.