Most people say they're tired when they skip their morning run or nod off during their favorite 9 o'clock sitcom. But if you want to know about real bone-crunching fatigue, the kind that chains you to your bed, ask someone with a thyroid disorder.

For me, the exhaustion was totally out of character. I'd always been high-energy, even a tad hyper. Six hours of sleep a night was enough. Then last fall I became a different person, someone I didn't like very much at all.

I'd get up at 7:15 and see my 13-year-old out the door, then lie down. Next thing I knew it was 8 a.m. and there were a mere 10 minutes left to get my 10-year-old fed and to school. As if her tardies weren't bad enough, I started crawling back into bed again after I dropped her off. Suddenly there weren't enough hours in the day to earn the living that supported us all.

Though I mentioned the problem to my doctor, all he did was offer sleeping pills. But then my younger sister discovered she had a thyroid problem, and her doctor said it runs in families. (Health.com: Why thyroid disorders are so common )

I read a list of the possible symptoms -- exhaustion, depression, constipation, hair loss, and heavy periods, among others -- and all the pieces began to fall into place. I have hypothyroidism. I share the disorder with millions of Americans, most of them women. And today, in many ways, I'm luckier than most. Thanks to my symptoms and a family history, my doctor put me on thyroid medication.

Now, at 44, I'm back to my usual self. My fatigue and constipation are gone and my eyebrows are growing back. I'm lucky. Millions of people aren't getting the help they deserve. You may be one of them.

A thyroid epidemic?

The Colorado Thyroid Disease Prevalence Study, published in 2000, found that as much as 10 percent of the population may have a thyroid disorder, and as many as half of those cases were thought to be undiagnosed. Six years later, that's considered a conservative estimate. Some experts say a woman over 35 has a 30 percent chance of developing hypothyroidism. When I tell people about my condition, the room echoes. They say they have it, too, or report that a friend or family member does. (Health.com: Feeling sluggish? Try sushi )

What's going on?

New thinking seems to be uncovering many more people who suffer from hypothyroidism -- happy news, assuming they get treated. For decades the disorder has usually, but not always, been diagnosed with a blood test, a good place to start if you think you may have it (see "How to Find Answers," at right). In recent years the American Association of Clinical Endocrinologists recommended narrowing the so-called normal range for blood-test scores, catching millions more whose thyroid issues wouldn't have been diagnosed otherwise. Even if your results fail to flag a problem, you may still have symptoms and be a candidate for treatment. (Health.com: Help for hypothyroidism )

Hello, sluggishness

Your thyroid is a tiny, butterfly-shaped gland at the base of your neck. Sometimes described as the body's thermostat, it controls energy flow. Hypothyroidism, also called low thyroid, means the gland isn't producing enough hormones to do its job. The most frequent cause is Hashimoto's thyroiditis, a condition that causes your body to produce antibodies that attack the thyroid. A shortage of thyroid hormones makes you sluggish at every level.

Slowed digestion causes constipation, sluggish metabolism leads to weight gain and elevated cholesterol, even hair and skin can become dry and coarse (and hair can fall out) because they're not getting enough nutrients. The brain also needs thyroid hormones to use oxygen and stimulate the production of chemicals like serotonin and dopamine that regulate emotions. That's why hypothyroidism can lead to depression and moodiness, not to mention the fuzzy thinking that nearly every thyroid patient complains about. Other symptoms, such as heavy periods, cramps, and a queasy stomach, are trickier for doctors to connect to an underactive thyroid. (Health.com: Making sense of medical tests)

Most of these symptoms may sound familiar--it's not unusual for a 30-, 40-, or 50-something woman to feel tired, bummed out, and a little bit overweight -- and this makes hypothyroidism that much harder to diagnose. In many cases, doctors assume a woman is simply going through perimenopause or suffering mild depression. "It's all too common for a doctor to hear 'tired, moody, forgetful' and offer the patient a prescription for antidepressants," says Richard Shames, M.D., of San Rafael, California, a thyroid specialist.

There are few things more frustrating than getting the wrong treatment. My younger sister was told to take antacids for her nausea. Doctors didn't immediately recognize her hypothyroidism in part because she's thin and didn't feel tired. "It was awful," she says. "My husband would cook us a great dinner, I'd eat one bite and feel so sick I'd have to crawl into bed."

After doing her own research and insisting that her doctor give her a relatively new kind of test, my sister got an accurate diagnosis. It took a while to get the right dosage of medication, and that's not uncommon. (Treatment usually consists of replacement hormones.) But the nausea is gone now.

Good-bye, desperation

"I've seen so many patients come in with the same story," says Stephen E. Langer, M.D., a thyroid specialist in Berkeley, California. "From their symptoms, it's clear that their thyroid is underactive. But either it doesn't show up on standard tests, so their previous doctor refused to prescribe medication, or they are on medication but it's not working."

The desperation seems all the more unjust when you realize that being treated can be a life-affirming event. My friend Cathryn Jakobson Ramin, 49, a fellow writer from Mill Valley, California, is a wonderful example. A few years ago, she noticed that her hands and feet were always cold, her hair was falling out, and her memory was increasingly iffy. After a few years of being told her thyroid tests were normal, Cathryn found her way to a specialist. Once treated, she noticed a huge improvement in her memory.

At a recent party where hypothyroidism came up in conversation, several friends described unsuccessful attempts to get treated for symptoms that seemed suspiciously hypothyroid, while others raved about how much better they felt taking thyroid medication. Cathryn came up to the group, listened for a moment, then announced, "They should put it in the water."

Frequent Health contributor Melanie Haiken lives in Northern California.