'Selling Sunset' star says she felt like she was 'dead.' What is Hashimoto's disease?

This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis or treatment. Contact a qualified medical professional before engaging in any physical activity, or making any changes to your diet, medication or lifestyle.

Heather Rae El Moussa is opening up about her health journey following a diagnosis she received earlier this year.

Talking to TODAY, the "Selling Sunset" star says she was four months postpartum when she began noticing changes in her body. That included a major drop in her milk supply, as well as feelings of extreme fatigue.

"I remember saying to my assistant, 'I feel like I'm dead,'" the 36-year-old reality TV star says in an article published Thursday. "My brain was so tired. My body was so tired. I was exhausted all the time and no amount of sleep could make it better.

"Filming was absolutely brutal because I could barely get out of bed."

At first, she believed her symptoms were a part of motherhood. The "Flipping the El Moussas" star had given birth to her baby son, Tristan, whom she shares with husband Tarek El Moussa, 42, on Jan. 31.

"I was like, I'm probably just foggy because of 'mom brain,'" she shares.

After visiting a lactation consultant and getting some blood work done, the real estate agent's doctor shared results that left her in "total shock."

But what exactly is Hashimoto's disease and should new mothers be concerned about developing it? Read on to learn everything you should know.

What is Hashimoto's disease?

Hashimoto's disease, also known as Hashimoto's thyroiditis, is a chronic inflammatory disorder of the thyroid, according to the Thyroid Foundation of Canada. The thyroid is a small, butterfly-shaped gland that sits at the base of the neck below the Adam's apple, and produces hormones that help regulate bodily functions, primarily controlling the speed of your metabolism.

First described by Japan's Dr. Hakaru Hashimoto in 1912, the autoimmune disease typically results in hypothyroidism, which is lowered functioning of the thyroid. In Canada, the most common cause of hypothyroidism is Hashimoto's disease.

Hashimoto's disease is also associated with an increased risk of developing thyroid cancer, according to the Canadian Cancer Society.

What are the signs and symptoms of Hashimoto's disease?

Cleveland Clinic states people with Hashimoto's disease might not show any symptoms initially. But as the disorder develops, your thyroid gland may become enlarged, a condition called goiter. That's a common first sign of Hashimoto's disease, and while it may not hurt, it can make the front of your neck look swollen.

If Hashimoto's disease progresses, the following symptoms can occur over time:

• Fatigue and sluggishness

• Mild weight gain

• Excessive sleeping

• Constipation

• Dry skin

• Feeling cold

• Muscle weakness and aches

• Joint pain or stiffness

• Dry hair or hair loss

• Irregular or excessive menstrual bleeding

• Low mood or depression

• Memory problems or difficulty concentrating

• Decreased sex drive

What causes Hashimoto's disease?

Hashimoto's disease's is an autoimmune disorder, meaning your body's immune system attacks healthy tissues. In this disorder, your body creates antibodies that attack the hormone-producing cells in your thyroid, which usually results in hypothyroidism.

According to Mount Sinai Health System, Hashimoto's disease begins slowly, taking sometimes months or even years to be detected.

But what causes the immune system to attack the thyroid's cells isn't clear, Mayo Clinic notes. For some, it can be genetic factors. For others, it's an environmental trigger, such as an infection, stress or radiation exposure.

For "Selling Sunset" real estate agent Heather Rae El Moussa, it was her pregnancy that triggered the disease, according to her doctor.

"When she told me what I had, I was in total shock," she tells TODAY.

Who's at risk of developing Hashimoto's disease?

Women are 10 times more likely to develop Hashimoto's disease than men, according to Cleveland Clinic.

While the disease can occur any time, it typically starts during middle age between the ages of 30 to 50.

Your risk for developing Hashimoto's disease also increases if you have another autoimmune disorder, such as type 1 diabetes, lupus or rheumatoid arthritis. Cleveland Clinic also states that genetics account for up to 80 per cent of your chances of developing Hashimoto's disease.

What possible complications come with Hashimoto's disease?

If left untreated, there are a range of complications that can arise with Hashimoto's disease and hypothyroidism.

In terms of heart health, it can impact your heart function and cause irregular heart beats. Untreated hypothyroidism can also lead to high cholesterol, which creates a risk for cardiovascular disease and heart failure.

Mental health issues such as depression can develop early in Hashimoto's disease. A reduced libido may also occur, along with reproductive issues like an inability to ovulate in women or erectile dysfunction in men.

Hypothyroidism can also create problems during pregnancy, such as increasing the risk of miscarriage or preterm birth. Babies born to mothers with untreated hypothyroidism are also at risk of developing developmental disorders like autism or decreased intellectual abilities.

Finally, a life-threatening condition called myxedema could occur. Though rare, a myxedema coma slows down your body's functions and can be deadly.

How is Hashimoto's disease treated?

There is no cure for Hashimoto's disease. However, there are medications to help manage your thyroid hormone levels if you develop hypothyroidism.

In cases of the disease where you don't have clinical hypothyroidism, your health care provider will likely monitor your thyroid hormone levels instead of starting treatment.

If you do have hypothyroidism, you will likely go on a medication called levothyroxine, which will help regulate your body's thyroid hormone levels and must be taken daily.

Let us know what you think by commenting below and tweeting @YahooStyleCA! Follow us on Twitter and Instagram.