Had a very comfortable journey back from Portland, but despite that I'm still feeling a bit weird today. However, I did manage to sleep through last night, albeit with some periods of mild wakefulness. You can't cheat your body clock.
The thing about jet lag is that our bodies have rhythms. Quite a few of them. There's the 24 hour circadian rhythm, which then governs all these sub-rhythms. For example, hormones - the chemical messengers that coordinate many of the body's functions - are released in a pulsatile fashion. The information they contain is not just in their concentration, but also in the temporal information conveyed by the timing patterns of their release.
When we cross time zones the result is that this carefully coordinated timing is jumbled up. So not only do we sleep strangely, we also feel a bit weird. The circadian clock that regulates much of this rhythmic activity needs to be re-entrained, and so the best way to achieve this is to fit in with the new time zone as much as possible. Light is the main cue for entrainment, but food and excercise also work. The worst thing to do is take a nap or go to bed really early, because then the clock takes longer to re-set. [You can also take melatonin, but for this to work, the timings need to be pretty spot on, and combined with suitable light cues. Melatonin is available over-the-counter in the USA, but not the UK.]
Having said this, I recently met a scientist visiting New Zealand who, because he was there only a few days, didn't want to re-entrain his clock. The poor guy was trying not to fit into the new time zone, and was being extra careful not to expose himself to daylight. To me this seems a bit nuts. You don't often get to visit New Zealand from the UK, and even if it is just for a few days, you can't have much of a love for life if you hide yourself indoors with the curtains drawn.