Sleeping: When I was a kid I always slept on my back. But at age 15, likely due to long-distance cycling, I ended up having surgery to remove a huge pilonidal cyst located at the base of my tailbone. I was told that I couldn't sleep on my back for about 2 months, and I haven't been able to ever since. Either side or lying on my stomach is fine, but up until the last year or two, it was impossible for me to sleep on my back. Only recently have I managed to snooze a bit on my back while watching the tube. This was a real disadvantage as someone who did a lot of air travel. The ability to sleep on a plane would have made life soooooo much easier. I ended up buying an extra battery [power ports were not generally available yet on airplanes] for the laptop and watching tons of movies instead.
Can't stand to read for more than an hour or so on a plane either. I think the pressure changes make it difficult for me to focus.