Jet lag is a temporary sleep disorder that occurs when the body’s internal clock, or circadian rhythm, becomes out of sync with a new time zone. It happens after travelling quickly across multiple time zones, as the body struggles to adjust to the new schedule of daylight, sleep, and meals. The more time zones crossed, the stronger the effect tends to be.

Common symptoms of jet lag include fatigue, trouble sleeping, difficulty concentrating, irritability, and digestive issues. Some people may also feel disoriented or have headaches and mood swings. These symptoms usually appear within a day of travel and can last for several days until the body adjusts to the new rhythm.

Jet lag affects everyone differently depending on age, health, and travel direction. Travelling east tends to be harder because it shortens the day, requiring the body to fall asleep earlier than usual. Travelling west is often easier since it lengthens the day, allowing for a more gradual adjustment to local time.