I don't usually do this, but I found this article interesting for travelers or people with unsual sleep cycles (like myself).
http://parentingsquad.com/easy-way-to-reset-your-sleep-cycle-stop-eating.html While the point of this article seems to be to eliminate or reduce jet-lag, it could also be used to explain why sometimes your own sleep cycle can get out of wack, and how you might be able to correct it.