I've also been in this position. I've even gotten myself to the point where I'll be up all night and sleep all day because my sleep patterns get so out of whack. I also use it as a way to avoid reality, especially since when I sleep I don't dream, so to me, sleep is like a non-existence, which I (sadly) find very nice.

I recently started seeing a Pdoc, and one of the first things he had me do was to have my blood tested. I was actually anemic -- low on iron -- which causes you to be extremely tired. EXTREMELY tired. You might want to look into getting your blood tested. If anemia is the case, it's fairly easy to deal with. You start taking iron supplements and you should start to feel better in about a week.

Good luck
Ro