The end of the year is supposed to be a glorious break for me. I rarely take vacations that last longer than a few days (a habit to address another time), so the extended period off around the holidays is a dream. No responsibilities! No emails! Long stretches where I can binge-watch “Vanderpump Rules”!It’s also the time when I invariably get a monstrous cold and end up bedridden for a few days. Or stuck with a virus that follows me into the new year.It’s not just the winter when this happens: Tons of anecdotes from my co-workers, and a preponderance of gripes on the internet, suggest our bodies simply succumb to sickness the moment we take time off.What gives? Are we just cursed by timing, or is there something deeper going on? Here’s the expert scoop:Your vacation prep might actually be a culprit.AleksandarNakic via Getty ImagesYou might be in a state of bliss when you’re on vacation, but chances are the days leading up to it are anything but. Maybe you’re putting in long hours at work to prep for the days you’ll be out of the office. Or perhaps you’re skipping the gym to do laundry so you’re not visiting home with a suitcase of dirty clothes. (Just me?)These behaviors can throw your body ― and your immune system ― out of whack, according to Dr. Edo Paz, a physician for K Health, a primary care app, and clinical director at Heartbeat Health, a cardiovascular center in New York.“You may be more stressed, fatigued, etc. in the days leading up to a vacation while making all the arrangements you need to make before going on vacation,” he said.It’s important to keep up a balanced routine, even if you have an endless to-do list before you hit the road, Paz said.“Do your best to keep your immune system as strong as possible during this vulnerable time,” he said. “That means eat healthy, exercise, get plenty of sleep, keep your weight healthy and don’t smoke or drink alcohol in excess.”You could be experiencing the ‘let-down effect.’Maskot via Getty ImagesIt’s not just colds and the flu: Many people also notice an increase in mental health symptoms, chronic pain issues or other ailments when they’re relaxed. This is known as the “let-down effect,” and it typically occurs following an intense period of stress. As U.S. News & World Report put it in 2016:Research has linked the let-down of perceived stress with an increase in flare-ups of pain and other ailments. One study found that people experience more panic attacks on the weekends, and a 2015 study from Taiwan found that holidays and Sundays have more emergency room admissions for peptic ulcers than weekdays do.The best way to prevent this is to control your stress as much as possible in the first place. This can involve exercising, hanging out with friends, talking to a therapist or any other self-care routine available to you. (Here are dozens of other suggestions to browse.)Traveling itself can mess with your immune system.Nikita Myslivtsev / EyeEm via Getty ImagesThis one’s a bit obvious: You come into contact with a lot of people, and therefore a lot of germs, when you’re traveling through an airport or by train. That can make you more susceptible to getting sick.“Many of these infections spread by tiny droplets made by people with the illness, which can remain in the air or on communal surfaces,” Paz said. “This problem is particularly prominent on airplanes where there are a lot of people traveling in a small space with reduced air circulation and frequent traveler turnover.”To protect yourself, make sure to wash your hands often and try to keep up healthy habits while you’re en route. The seat you choose on the airplane may also make a difference, according to research.Other Ways To Keep Yourself Healthyd3sign via Getty ImagesAside from the tips mentioned above, Paz stressed the importance of prevention when it comes to illness.“First of all, get your flu shot. The CDC recommends that all people older than 6 months of age get the flu shot each year,” he said. (If you’re wary of getting the shot because you’re sick or you think it won’t matter at this point in the season, these myth-busters about the vaccine should clear that right up.)“Other than that, practice good hygiene,” Paz said. “Wash your hands frequently and clean and disinfect commonly touched surfaces.”If you’re already sick, assess how you feel before traveling. Setting off on a trip while ill could make your health worse and hurt others around you. And if you do decide to make the journey, “make sure to cover your sneezes and coughs with a tissue or your upper sleeve, [and] throw away all used tissues,” Paz said.Otherwise, the only adventure you’ll be taking on your trip is from your bed to the pharmacy.