Springtime vacations to faraway destinations, at best, can leave you with sunny memories and a sun-kissed glow. At worst, you could return with nightmares of travel gone wrong, a painful sunburn, debilitating jet lag and even … long-term memory loss.

Sure, it’s normal to feel groggy a few days after a long flight across time zones. But researchers from the University of California at Los Angeles discovered that memory and learning problems may persist a month after returning — not exactly the souvenir you wanted to bring back with you.

The researchers subjected hamsters to six-hour time shifts and measured their memory and learning ability. The hamsters had trouble learning simple tasks, and what’s more, the disabilities lasted a month even after the rodents had returned to their normal sleeping schedules.

The study also found that jet-lag caused permanent changes in the hippocampus, an area of the brain responsible for memory. The results lend explanation to why shift workers and airline attendants show slower reaction times and higher rates of diabetes, heart disease, hypertension and cancer. They can even experience reduced fertility.

The culprit? A disrupted circadian rhythm, the biological clock that regulates when we wake and fall asleep. For each time zone crossed, our bodies can take up to a day to catch up — and the more distance traveled, the worse the symptoms.

So what’s a time zone-hopping traveler to do? First, try to acclimate to your destination’s time before you arrive. For example, if you’re traveling to New York from L.A., hit the hay earlier for a few nights before you leave. Stay hydrated in flight and eat balanced meals. Lastly, expose yourself to bright natural light when you feel yourself getting drowsy too early. Sunlight shifts your circadian rhythm — and can help you remember those blissful days on the beach after your next vacation.