I hope this question is not too silly, but I have been on some long flights, and found I cannot sleep sitting upright. I can close my eyes and relax, but sleep doesn't come. It is the same thing at home as well. Can one train themselves to sleep upright on a plane? Is this a mental block? Do any other travelers have this problem, and how can I remedy this? I am going to Australia.
Can you train yourself to sleep upright, yes. But is it worth it?
People all over the world adapt to sleeping in various position, on hard cement floors, V shape in hammocks, on pillow beds, in broad daylight, etc. It is basically a matter of doing it day after day until your body adapts. But do you really want to spend a couple of weeks without good sleep adjusting to napping in a chair for just one flight?
I, like yourself, can not sleep upright and I make numerous long haul trans-pacific flights each year. I just accept the fact that I will tired upon arrival and plan my schedule accordingly.
The way many people solve this, or at least attempt to, is by using a neck support, and then alcohol or drugs. Ideally if you take any form of sleep inducing pill, you should take it after you take off in case the flight returns to the gate and you need to deboard. If you do choose to take this route, I'd recommend trying your chosen strategy before your first attempt on a long haul flight, in case you have a negative reaction in some way.
It's definitely not recommended getting drunk before a flight as you may be refused boarding, however 2 or 3 drinks may sufficiently relax you in order to assist with sleeping. Only you will know how that works for you.
It's also worth considering that if you fly often, there may be ways to get reasonably priced business class flights or ways to upgrade to business class in order to get a flat bed. I'm currently on a trip in business class that cost less than economy would have been without a Saturday night stay. I was willing to give up a day of my weekend in order to have a bed.