Can't sleep

Even though I ran my ass off today at work, I can't sleep. It was so busy today and my body is exhausted. But, when I lay down to sleep, it just didn't happen. Then my friend Sarah came over for about an hour, and now I'm still wide awake!!! What is wrong with me? I didnt go to sleep till 7:30 yesterday morning and got up at one. I should be tired!!! My body clock sucks balls.