Ever wonder to yourself why you feel alone even in a crowded room? Even in the midst of family and friends, all of us can feel alone and lonely. After all, from Elvis to Cher to Akon, musicians have been crooning about loneliness for years.

Do you know the definition of loneliness? According to the Merriam-Webster online dictionary, loneliness means being without company; cut off from others; sad from being alone.

That's because the emotions that get set off when you're feeling alone can be quite powerful — they can trigger dejection and depression, and in extreme cases, loneliness can lead to earlier death, says John Cacioppo, PhD, a psychologist from the University of Chicago in Illinois.

According to the Mayo Clinic, having a strong social support network is essential during tough times, whether from job stress or a year filled with loss or illness. A social support network is comprised of family, friends, and peers. Having intimate relationships with others helps you feel cared for and maintain optimism, and aids in stress management. All of these emotional benefits lead to stronger immunity to help you fight disease and stress.

Alternatively, according to Dean Ornish, MD, in his book Love and Survival: The Scientific Basis for the Healing Power of Intimacy, among heart patients, depression is as good a predictor of imminent death as smoking, obesity, or a previous heart attack.

"Study after study shows that people who are lonely, depressed, and isolated are three to five times more likely to die prematurely than people who feel connection in their life,” says Dr. Ornish.

In a Duke University Medical Center study of 1,400 men and women with at least one severely blocked artery, the unmarried patients without close friends were three times more likely than the others to die over the next five years. Similar findings came in a Canadian study of 224 women with breast cancer. Seven years after diagnosis, 72 percent of the women with at least one intimate relationship survived; only 56 percent of those who did not have a confidant survived. The kind of intimacy necessary appears to be an emotional connection to someone, not necessarily a sexual relationship.

Another supporting study, published in the Journal of the American Medical Association revealed that people with more diverse social networks (less social isolation) have a greater resistance to upper respiratory infections.

But how do you resolve loneliness? Everyone feels a little lonely now and again, and experts say that this forlornness can actually be a good thing, as long as you do something about it. "Loneliness is actually an evolutionary adaptation that should spur us to get back to socializing, a state in which we are happier and safer," says Dr. Cacioppo.

Could you be lonely without even realizing it? These signs point to "yes."