Restless

Restless; a Sleeping Simulator

You are tired; therefore you must slumber. Sleep doesn't come easy however. In order to fall asleep you'll have to balance how hard you're trying to do exactly that. When you're not trying to fall asleep, you won't. When you're trying too hard, you might keep yourself awake as you're frustrating yourself by doing so.

Even if you manage that you might get woken up right before you doze off because of some sudden noise. You have no control over when a mosquito flies by your ear, and while you have some influence over it, it sure feels like it is completely out of your control whether you'll be able to get a good night's rest.