9 Symptoms You Should Never Ignore

3. Unexplained Weight Loss

The big worries: Losing more than 5 percent of your body weight — without trying — over a period of six months could mean cancer: Weight loss is a symptom in up to 36 percent of cancers in older people. "If you or a family member is suddenly losing weight after trying 400 times before, you have to ask, 'Why is this time the charm?' " says Lichtenfeld.

What else it might be: Endocrine disorders are a common cause of unintentional weight loss. Of those with an endocrine disorder (especially hyperthyroidism, an overactive thyroid), up to 11 percent experience weight loss. The condition also triggers restlessness, sweating, increased appetite and difficulty concentrating.

If your weight loss is accompanied by extreme thirst or hunger, fatigue and frequent urination, it could be a sign of diabetes.

Gastrointestinal conditions like inflammatory bowel disease and celiac disease cause weight loss as well — in addition to symptoms such as diarrhea and abdominal pain.

Depression and other psychiatric conditions could be to blame, too. "Decreased appetite and weight loss are very common symptoms of depression," says Susan G. Kornstein, M.D., professor of psychiatry and obstetrics/gynecology at Virginia Commonwealth University. "But patients with unexplained weight loss should undergo a workup to rule out general medical causes."

4. Unusual Bleeding

The big worries: Ulcers and colon cancer can cause rectal bleeding or black or tarry stools, says Andres Pardo-Agila, M.D., a family medicine physician at the University of Texas Health Science Center at Houston. If you haven't had a colonoscopy recently, talk to your physician. Vaginal bleeding can be linked to gynecologic cancers. Bloody vomit can result from stomach or esophageal cancer, and people with lung cancer can cough up blood. "Whenever you see blood where it shouldn't be, see a doctor," says Lichtenfeld.

What else it might be: Blood in the stool may be due to hemorrhoids, while blood in the urine may be the result of a bladder or kidney infection. Vaginal bleeding long after menopause may be due to the growth of benign polyps or fibroids. Vomiting blood can result from a tear in the blood vessels or an ulcer in the stomach or esophagus. And coughing up blood can happen with noncancerous conditions, like bronchitis, pneumonia or tuberculosis. "There are many common reasons for seeing blood where you don't expect it, but it still has to be checked out and treated," Lichtenfeld advises.

5. High or Persistent Fever

The big worries: Fever is your body's way of fighting infection. But "fever of 103 degrees and higher warrants a trip to the doctor — period," says David Bronson, M.D., president of the American College of Physicians. It may indicate a urinary tract infection, pneumonia, endocarditis (inflammation of the lining of the heart chambers and valves) or meningitis, which may require antibiotics to clear up. A persistent low-grade fever — for several weeks — with no obvious cause is characteristic of some infections, including a sinus infection, and some cancers, like lymphoma and leukemia. "Cancer is on the list of things we think about, but it is usually not the first thing," says Ronan Factora, M.D., a geriatrician at the Cleveland Clinic in Ohio.

What else it might be: Fever can be triggered by a virus, which, depending on your health and other symptoms, may require hospitalization.

Next: Shortness of breath. »