You ahve something called a sleep debt - an accumulation of all the hours of sleep your body needed that you didn't get. This NEVER GOES AWAY, unless you get extra sleep. When you have a high sleep debt you go to sleep quickly, when you have a low sleep debt it can take longer.
Also - your body kicks into high gear in the second half of the day, keeping you awake (accumulating your sleep debt) so you will be physically able to sleep for eight hours at once (or however long). It's REALLY hard to go to sleep before this system (CDA, aka Clock-Dependant Alertness) shuts down.
Brought to you thanks to Dr. Dement, HUMBIO 11 (Sleep and Dreams), Stanford University.
Rand al`Thor
Elayne Trakand's Warder and Alexia's Guardian!