mehn.. i feel your pain. i am a student and i know how most of this stuffs happens. sometimes this sleep something will just come from no where and will make you look like a drunkard...lol
maybe its because you refuse to submit the assignment in your dream and thats why you are going to write another one. you should have easily go to bed, sleep and dream, make sure you see yourself submitting your exam paper before waking up..lols