Sleep

The reason so many people have trouble getting to sleep is because those in charge don't really care about them. The school administration caters to the whims of the working parents, who would probably be happier if school started even earlier. Also, teenagers are given a lot of homework, which, coupled with any after-school activities, makes going to bed at a reasonable hour all but impossible. Essentially, the world is too competitive nowadays. Some schools are considering lengthening the school day. Too much homework is assigned on a daily basis. I myself don't usually finish my homework until 9:00 or 9:30, and I can't just go to sleep afterwards. (I would be completely and utterly miserable if I did.) To show the absurdity of the competition nowadays, just look at PV's AP Physics course. It starts at 7:00 in the morning. I'm still getting out of bed then! Sure, some kids may take it because they want to, but I'm sure one of the main reasons is that it looks good on a college application.
I think the other problem is that we a as a society have glorified sleeplessness - the employee who works through the night without sleep is preferred to the one who goes home at 8:00. Arriving at work earlier is considered a sign of punctuality, not insanity. Sleep is too often viewed as a useless period of lethargy during which we could be accomplishing work, rather than as the biological necessity it is. This is the main problem with our society.