Everyone's biggest fear when stepping in a doctor's office is coming out with an illness they never knew they had.

One of my friends had been complaining of intense stomach pain for months. She visited the doctor regularly to get blood work and was on stress pills for quite some time. She even got an endoscopy, where they inspected her stomach from the inside to see if there was anything wrong.

They discovered nothing.

After months of what she described as pure agony, my friend was referred to a gynecologist, who shed some light on what's been going on.

Turns out it wasn't her stomach that wreaking havoc on her health, it was her baby making parts.

According to the American College of Obstetricians and Gynecologists, anyone who has their period is at risk of developing a condition known as endometriosis.

It's estimated that 1 in 10 women have it, and they may not even know they do. Some women show obvious signs, like my friend, and others may not show any signs of the condition at all.

Some celebrities have been coming forward to speak about their personal struggle to raise awareness about this condition.

Dancing with the Stars dancer Julianne Hough recently opened up to E! News, revealing how she has been suffering "in silence."

Singer-songwriter Halsey also has been suffering with the condition for years, saying she has had to go "backstage in the middle of my sets, or fighting back tears on an airplane, or even being in so much pain [that she] would vomit or faint."

Scary stuff. Here's all you need to know about this mystery illness:

What is endometriosis?

This condition causes tissue that's supposed to be on the lining of your uterus to grow outside of it. Over time, this tissue will get thicker and bleed every time you are on your period. The issue here is that while you're bleeding regularly, you're also bleeding internally, which is wreaking havoc in your lower abdomen region.

So it's no surprise why some women have terrible pains, but that's not all...

Symptoms

Common symptoms, aside from having terrible period pains, includes painful urination and bowel movements, heavy periods, and still bleeding right after your period cycle ends.

Mary Jane Minkin, M.D., a clinical professor in the Department of Obstetrics, Gynecology, and Reproductive Sciences at the Yale University School of Medicine, told Glamour that everyone who suffers from endometriosis experiences pain differently, which is why it's hard to diagnose.

"Endometriosis can present with gigantic"”I mean basketball-size"”cysts on the ovary, and the woman can have zero pain," Minkin said. "Then some unfortunate folks have implants of endometriosis that look like cigarette powder burns, and they can have awful pain."

Treatment

Anti-inflammatory drugs like Advil can work to minimize pain, but if the pain is relentless, surgery may fix the problem.

That being said, endometriosis tissue may grow back, and in some cases people have had to get a hysterectomy to prevent them from getting the condition again.

Have you heard of anyone suffering from this condition before? Share this article to spread awareness about endometriosis.

[H/T: Glamour]