TENSION: Celine dion unintentionally attempted suicide through drug abuse… See details

Celine Dion opens up about her struggle with Stiff Person Syndrome in her new Amazon Prime documentary. Dion says she tried to perform through pain by increasing her medication dosages, especially Valium.

After managing undiagnosed stiff-person syndrome symptoms for 17 years, Céline Dion is looking back at her health journey through a lens of gratitude.

In PEOPLE’s latest cover story, the music superstar, 56, opens up about the progressive symptoms that began manifesting in the mid 2000s, including muscle spasms, difficulty breathing (and thus, singing) and, most severely, “crisis” episodes during which her entire body locked up that caused excruciating pain.

The first time she felt a spasm nearly 20 years ago, she was in Germany on tour. “I had breakfast, and I suddenly started to feel a spasm. My vocal exercise made it worse,” recalls Dion, who is giving fans an in-depth look at her fight against SPS in an emotional new documentary, I Am: Celine Dion that (streamed globally June 25 on Prime Video).

Dion tried remedies ranging from steam showers to over-the-counter medications, and made appointments with ear, nose and throat physicians and ophthalmologists, all of which were unfruitful.

As her symptoms intensified, the “My Heart Will Go On” singer — beloved for her vocal precision and inimitable stage presence — was advised to take prescription medications, including muscle relaxers like Valium.

“We started with two milligrams to see if it would help, and then 2.5, and then 3, and 15 and 50,” says Dion, noting the medication began wearing off so quickly that at one point she took 90 milligrams of Valium to power through a performance.

“I did not understand that I could have gone to bed and stopped breathing,” the superstar tells PEOPLE in its latest cover story