Have you ever wondered how you manage to get through a particularly stressful period – whether it's an intense deadline at work, final exams in school or a spate of holiday houseguests – only to get sick after the stress has lifted?

It's not a fluke. It's a phenomenon that's often referred to as "the let-down effect," a pattern in which people come down with an illness or develop flare-ups of a chronic condition not during a concentrated period of stress but after it dissipates, explains psychologist Marc Schoen, an assistant clinical professor of medicine at the University of California–Los Angeles and the author of "When Relaxation Is Hazardous to Your Health."

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.

In a 2014 study, researchers from the Albert Einstein College of Medicine in New York had migraine sufferers track their symptoms and stress patterns in a three-month electronic diary; it turned out that participants' stress levels didn't impact migraine occurrence, but a decline in their perceived stress from one evening entry to the next entry was associated with increased migraine onset over the following six to 18 hours – evidence of what the researchers call a "let-down headache." The let-down effect can also happen with flare-ups of asthma, autoimmune diseases (like lupus and Crohn's disease), digestive problems and skin conditions (such as eczema and psoriasis), Schoen says.

It's long been known that stress can lead to illness but only recently has evidence emerged that some people tend to get sick after a pressure-packed period has ended. To understand how and why this can happen, it helps to review how stress affects the body.

During acute stress, the body releases key hormones – including glucocorticoids (like cortisol), catecholamines (like norepinephrine) and adrenaline – to prepare itself to fight or flee from danger and to trigger the immune system to step up certain types of surveillance. In the process, "glucocorticoids can reactivate latent viral infections such as herpes simplex 1 [which causes cold sores] and Epstein-Barr virus [which can trigger fatigue, fever, sore throat and swollen glands], for which symptoms are only obvious after a few days," explains behavioral neuroscientist Leah Pyter, an assistant professor of psychiatry at The Ohio State University Medical Center in Columbus. That's why the symptoms may appear after the stress lifts – say, over a weekend, on vacation or after an exam period.

Meanwhile, while you're under pressure, the rise in cortisol and other stress hormones can protect you against the perception of pain, which is helpful in the moment because it can help you reach safety in a dangerous situation without being hindered by pain, explains psychologist Dawn Buse, director of behavioral medicine at the Montefiore Headache Center and an associate professor of neurology at the Albert Einstein College of Medicine. "After a stressful period has passed, the body returns to a state of normality and many of the systems that were activated calm down," she says. "This includes a drop in cortisol as well as other stress hormones [which could] set the stage to initiate a migraine." Similarly, that post-stress drop in cortisol could trigger a flare-up of other forms of chronic pain, such as fibromyalgia and arthritis.

Another way the sudden decrease in pressure can set you up to crash and burn: "Emotional stress and physical stress kick up the same inflammatory response, which opens the door for illness or the let-down effect," Schoen explains. After either type of stress dies down, there's "a down-regulation of the immune system, a suppression of the immune response, [as a reaction] to the easing of stress." In addition, the surge-and-fall of stress hormones could knock down dopamine levels in the brain, which can trigger overeating and substance abuse as people (unconsciously) try to raise their dopamine levels so they can feel reward and pleasure again, Schoen explains.

One of the best ways to avoid the let-down effect is to prevent the strain from getting to you in the first place. You can do this by pacing yourself when you're under pressure, getting plenty of exercise and sleep, eating healthfully and taking time to decompress on a regular basis (with meditation, rhythmic breathing or other relaxation techniques), says Dr. Nieca Goldberg, medical director of the Joan H. Tisch Center for Women's Health at the NYU Langone Medical Center. "During a stressful period, have a plan that calls for breaks as you go through it" so that you're not revved up 24/7. Indeed, the body's "fight-or-flight response can be deactivated quite effectively through diaphragmatic breathing and guided visual imagery," Buse says. "Someone who has high levels of stress at work could simply take 30 seconds to focus on their breath between meetings and appointments and try to avoid the build-up of stress that could happen over the course of a day."

If it's too late for a pre-emptive approach, you can mitigate the let-down effect by helping your body de-stress slowly. "Just like you have a cool-down period after exercising, you want your body to have a tapering down of stress," Schoen explains. The key, he says, is "to keep your body slightly revved up to keep your immune system from downshifting abruptly" when the stress ends.