For starters, everyone and every flight is different. Some people adjust to jet lag really well, and some don't. Similarly, some flights are timed really well and some aren't. This could be due to flight length, (which we'll get into in a second), airport curfew or any other of the hundreds to thousands of factors that must be taken into account when an airline plans a flight. Also, as for the East to West and West to East thing, there's actually a term for this. For most intercontinental flights (flights that range about 4-7 hours in length) that are heading to the East from West and are departing during the night, they are called Red eye flights. The problem with these flights is that they depart at say 12:00 am from LAX and arrive at NYC at 8:45am, but the fight was only about 6 hours. This occurs due to time zone changes. Because of this, you do not really have sufficient time to get a full nights rest on the flight (it being only around 6 hours long) but a full night's time has already past. These flights are most common in North America on routes such as Los Angeles to New York City or from Vancouver to Toronto, though other regions may also have these flights. On the contrary, when flying from the East to West, the flight time is also 6 hours, but due to the time one difference, only two to three hours has "passed". So instead of not having enough time to sleep, one actually gained extra time to sleep. For example, a flight may depart NYC at 12:00pm, and will arrive in LAX at 2:50pm. Only two and a half hours has elapsed, but the flight itself was six hours long. Hope you understood it!