That explains why I slept so well when I was locked up (back as a young'n in juvie): You didn't have control of the light in your cell, so from ~10pm to ~7am lights were out whether you liked it or not. I'm a life-long insomniac.
The reverse - going to sleep as the sun creeps up - is difficult for me. It feels worse to me to try to sleep as dawn comes than just an hour earlier.
I'd expect to fall quickly and pleasantly asleep after an all-nighter, but the combination of dawn, the pounding of my heart and racing of my mind actually leave me awake and thinking for an extra few minutes. It's possible that going to sleep in that state gives me extra insight on what I was working on, but it doesn't feel good.
Interestingly, the effect of light on the biological clock reverses in the middle of the night, so that light in the early morning tends to make the cycle shorter. Which I guess also makes sense since that's how it would have to work with jetlag.
