Is jet lag ever an issue for you?
Every individual responds to jet lag differently. Age, sleep cycle, flight times...etc can make a difference.
A friend of mine once told me she'd never had jet lag problem. She flew between U.S. and Asia.
See if these threads help:
http://www.flyertalk.com/forum/trave...-approach.html
http://www.flyertalk.com/forum/trave...messed-up.html
http://www.flyertalk.com/forum/trave...australia.html
http://www.flyertalk.com/forum/trave...s-germany.html