Hey Lynda,
Yeah, what Jeffe said. Everyone is different but we all have the same physiologic make up with variables between us. One of the pathways is regulated by melatonin. I starts to be released as low light conditions occur. (DiLMO dim light melatonin onset) within 1.5 to 2 hours after DiLMO the pressure to sleep increases and continues until dawn. I'm sure you've experienced that pick up in energy during a 24 hour event right before dawn.
Then there is the issue of body core temperature. As core temperature drops sleep onset is stimulated.
Also, some new research shows people who tend to like to get up early vs "night owls" perform less optimally during sleep deprived situations.
Don't forget caffeine. It can help to a point. To be most effective, a withdrawl of caffeine several days before an event makes it more effective.
Also there is sleep before an event. Short yourself, and you need it that much sooner.
As you can see, tons of variables, and I've just scratched the surface.
I think for me, the hardest is going through the night. As I was walking the steeps, I think that helped. Just getting off the bike and doing something different helped. That's what those sand traps are good for
.
It's gonna hit you at some time, the need to
. As Jeffe said a short nap can do wonders.
Hope that helps,
Dave