Jet lag is the closest experience that modern day humans have to time travel, but it's not as glamorous or useful as the Jetsons and Doc Brown made it look. In fact, jet lag can be just plain miserable. Even if you think you have your jet lag-busting techniques figured out, it can still be somewhat jarring on your body and health, and especially when you travel in certain directions around the world.
For a refresher, jet lag is your body's natural reaction to being thrust into a different time zone. We all have "circadian rhythms," which are physical, mental, and behavioral cues that sync up with the sunlight and darkness throughout the day, according to the National Institute of Health (NIH). But these delicate rhythms are disturbed when you travel to different time zones. While your body's internal clock adapts to the new time zone, it's common to feel tired, struggle with acute insomnia, and have some stomach issues. These symptoms are what's referred to as "jet lag."
Any time you travel across at least two time zones it's possible to get jet lag, but research suggests that traveling from west to east — for example, flying from Los Angeles to New York City — makes the effects worse. The reason? When you travel in this direction, you "lose" time, whereas traveling in a westerly direction will add time to your day.
Studies on jet lag have shown that the body needs a little bit more than 24 hours to go through its full internal clock. So, when you seemingly have more hours in the day, your body can handle the abrupt circadian change, whereas when you have fewer hours it feels harder to catch up. That's not to say that flying from the east to the west doesn't come with its own challenges, but it's just that the easterly flights tend to cause more severe jet lag effects.
Jet lag is an unavoidable reality of travel, and if your summer vacation plans include a trip headed to an eastern location, you're not doomed. It's just extra important to pay attention to your sleep habits ahead of and during this type of trip. That means sleeping on the plane, staying on your new timezone schedule, and doing what you can to stay awake until it's dark outside. If you do feel the effects of jet lag, you'll want to hydrate, exercise a little bit, and spend time in sunlight to combat the symptoms.
And although you might feel groggy and out of it in your more eastern location, the good news is that you'll hopefully have an easier time when you fly back the other way.