There is something truly annoying about having lots of things to do, going to bed and then finding yourself wide awake, hoping that it'll be morning soon so you can do those things. After lying there for three hours and coming to the conclusion that your sleeping isn't going so well you think "well maybe I should go up and do that thing!" but now you've been in bed for so long that it would be ludicrous to do so! You might fall asleep at any moment. Now you become irritated that you wasted all these hours lying in bed, not sleeping when you could have done that thing. Now you're just upset instead, sleep becoming even harder to achieve. About an hour after this you fall asleep and you wake up at shit o'clock.
Annoying, isn't it?