Sleeping on an airplane?

I have to know if there is some secret to sleeping on an airplane? Can one actually get good rest while crammed into a tiny space and sitting upright?

I personally cannot sleep on a plane. Try as I might, I just can't do it. I have tried sleeping pills, neck pillows, ear plugs and eye masks and nothing works. I sit by the window and try to lay my head against the wall and the arm rest juts out into my side. I sit on the aisle and try to lay my head this way and that...nothing. For short flights, I really don't mind. But it's the longer ones, usually coming back to Scotland from the States that I NEED sleep.

So I pose the questions to you. Can you sleep on planes? What is the secret? What do you do to get most comfortable? Share your airplane sleep success.