Is it writer's block or is my brain just not working today?

Once again my uni work is giving me some trouble. I'm really struggling to write my crit theory essay. It didn't help that all the books I needed had all ready been taken out of the LRC and my tutor demand to see a plan with a draft by next lesson. My mind keeps wondering to other things and I just seem unable to form the words to type on the blank screen, which seems to be taunting me with its whiteness. The fact I also feel sleepy and perhaps coming down with something.... also doesn't help me. I wouldn't really mind the fact I can't write it but it also seems to have effecting my other writings and with my normal stress reliving technique gone, I'm find that its worrying me a lot more then it should be. It the minute I'm feeling kind of numb, sort like I've no energy and the world of nice dreams and relaxing is calling to me. I've a day left for my essay, it can wait just a little longer, maybe its time to let the wings of sleep bore me away to a place of no worries?