YOU FEEL: A sting in your gut.

THE REASON: Rejection activates one of the same areas of the brain as physical pain, according to research from the University of California, Los Angeles. In one study, the more snubbed people felt, the more activity there was in the anterior cingulate, the region of the brain that registers the distress of physical pain.

WHAT TO DO: Tell your friends how difficult you're finding it. Putting your negative feelings into words lessens the activity in the pain-feeling part of your brain, says study author Naomi Eisenberger, Ph.D. Spending time with people you feel close to also helps the brain release opioids--the same painkillers found in opium and heroin, says Eisenberger.

In addition, some researchers suspect that the soothing feeling of being with others is vestigial: It may have prevented ancient humans from isolating themselves, which would have been dangerous to their survival. If all your friends are busy, go to the gym: Working out releases opioids, too.

YOU FEEL: Chest pain, as if you're having a heart attack.

THE REASON: A tragic or shocking event like a breakup can reduce the amount of blood your heart pumps. That can lead to symptoms such as chest pain and shortness of breath, say researchers at Johns Hopkins University School of Medicine, who have dubbed the phenomenon "broken-heart syndrome."

WHAT TO DO: Seek medical help immediately; emotional stress or anger can precipitate an actual heart attack. Scientists aren't yet clear about why some people are susceptible to brokenheart syndrome, but they know it affects more women than men, says Ilan Wittstein, M.D., assistant professor of medicine at Johns Hopkins. A buildup of stress hormones may precipitate this problem, so you could try regularly practicing relaxation techniques, such as deep breathing, meditation, or writing down your feelings in a journal (blogging might even help).

YOU FEEL: Like you get every cold and flu bug.

THE REASON: When you're preoccupied with a breakup, your stress-hormone levels can go up and your immune system could become unregulated, says Janice K. Kiecolt-Glaser, Ph.D., a professor of psychiatry at Ohio State University. In fact, Kiecolt-Glaser's research suggests that people who have recently separated or divorced have poor immunity for up to a year after the breakup--especially if they ruminated about the relationship afterward.

WHAT TO DO: Vitamins and herbs are not yet proven to prevent illness. So your best defense against colds and flu is advice you've already heard (because it works!): Wash your hands frequently. Go get a flu shot. And get the proper amount of sleep: Your immune system takes a hit when your sleeping patterns are disrupted. In fact, immunity is cut in half when you get 40 percent less sleep than you're used to. If your ruminating is causing you to lie awake at night, consider playing a video game. Some research suggests that the short-term, acute stress of the game helps boost certain components of your immune system.

YOU FEEL: Like you have trouble concentrating on anything.

THE REASON: Your brain changes when you're distraught about losing someone. A recent study in the American Journal of Psychiatry showed that women who hadn't gotten over a six-plus-month relationship by 16 weeks after the breakup had decreased brain activity in the regions associated with emotion, motivation, and attention.

WHAT TO DO: Try having an imaginary conversation with him. Confront him about your anger or regrets, and appreciate what he meant to you. This is more effective than actually talking in person, because you won't edit yourself to say what's appropriate rather than what's really on your mind. "The opportunity to say good-bye is cathartic, and it will clear your mind," says Holly Prigerson, Ph.D., an associate professor of psychiatry at Harvard Medical School. In fact, a recent article in the Journal of the American Medical Association found that people who included imaginary conversations like these as part of their therapy had more relief from grief than people whose therapy didn't include this technique.

THE HIGH COST OF STAYING TOGETHER

Breaking up is hard on your health, but staying in a bad relationship could be worse. Studies suggest that women who are dissatisfied with their marriages are more likely to develop risk factors for cardiovascular disease, such as hypertension, than their happily married peers. They're also more likely to have anxiety disorders, to take longer to heal from wounds, and to pay significantly more in health-care costs, says Prigerson.

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