Jet lag is a temporary sleep disorder that occurs when a person's internal body clock is out of sync with the time zone they are in. This often happens after long flights across multiple time zones, such as traveling from New York to London. Symptoms can include fatigue, difficulty concentrating, and trouble sleeping. The body’s circadian rhythm, which regulates sleep and wake cycles, can take several days to adjust to a new time zone. To help alleviate jet lag, travelers can gradually shift their sleep schedule before departure, stay hydrated, and expose themselves to natural light upon arrival.