I am usually procrastinating sleeping because if I won't wake up soon enough (6-7 hours) I am probably going to end up with a mild headache which will usually runaway into head splitting migraine. So the fear that tomorrow may be the day full of pain is keeping me awake from inevitable sleep.
I put off going to sleep because there's always the chance, no matter how small, that Gisele Bündchen might turn up at the door, and how would you feel if you woke up the next day and found you'd missed your chance because you were asleep?