hmm, well thanks for the information all
after searching google for "oversleep" enough, I discovered that there is actually a condition known as hypersomnia:
http://www.psychnet-uk.com/dsm_iv/hypersomnia.htm
They say on that site that it may relate to shiftwork, since your rhythms get all messed up. I've been having the worst headaches lately too...I guess the key here is just to force yourself to get up, which is what I haven't been doing. I'm not sure if I actually have that condition, but I guess i'll just try my best to avoid sleeping too long.
And a word of advice to everyone: shift work sucks. It's much better to be forced into being a morning person than having to creep around the only time you feel awake so you don't wake the family.