Sleep, whats that?

I really wonder why it is that I could lay down just about anywhere in the middle of the day and sleep soundly. At night I'm generally over tired, during the day I'm barely able to keep my eyes open and yet I will toss and turn all night long. Its most likely due to my acing body, general stress, and anxiety from the day. But how does one break this cycle? I mean on the days that I could possibly sneak in a nap, I don't simply because I fear for what my night will hold for me. Still no Sandman...