Just to echo everyone else, I just did the day flight from SEA to LHR yesterday, didn't really manage to sleep on the plane so landed at LHR at about 8 AM (outbound was delayed) and then had to wait 3 hours for my connecting flight to EDI. Even being in the CCR couldn't help the fact my body thought it was about 1 AM and just wanted to sleep. Spent the connecting flight feeling physically ill like I wanted to be sick from lack of sleep.