Lady Gaga Details Intense 'Pain' of First Oscars Rehearsal: 'I Could Barely Get Myself Together'

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Before the triumph of Lady Gaga's show-stopping Oscars performance, there was an intense and painful first rehearsal.

The 29-year-old pop star moved audience members to tears as she sang her Academy Award-nominated song, "Til It Happens to You," on the Dolby Theatre stage on Sunday, joined by a group of about 50 sexual assault survivors. In an Instagram post on Tuesday, Gaga poses backstage at the show with her arms around two of the female survivors. In the caption, the singer details the intense "pain" surrounding her first rehearsal with the group. Read the full caption below.

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"The first day of rehearsal with all the survivors I could barely get myself together. My body was wrecked with inflammation and pain, crying and shaking the whole walk to the stage. The whole night before I did not sleep. The fear of knowing I would finally face that I belonged in that group. I told them I was so sorry I couldn't be Lady Gaga for them, that I couldn't even get dressed. I could barely get through the song, couldn't hit any of the high notes. Hair wet, sloppy tee shirt jeans uggs, tissues. They all hugged me and told me that it was okay because it was more real this way, that they understood that they were in pain too. They told me they were there for me to support me because they believed this message needed to be heard. Without them I never could have felt strong. They accepted me for me, at my lowest and that was good enough for them, so somehow through the magic of their courage they made it good enough for me too."

ET spoke directly with one of the survivors, Kirat Sandhu, on Monday.

"She made a point to say to us, you know, we are helping her get through it. She's helping us heal, and we really wanted it to be an empowering moment for all of us and all the survivors that were watching," Sandhu said of that first meeting with Gaga.

"[Gaga] kinda brought us into a group huddle ... it was just a one-on-one conversation with all of us and she said how much it meant to her that we were there," Sandhu recalled. "The first time we saw her, she was sobbing. She could not believe that this had been made possible, that we were all there. That we were getting to do this with her."

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"Til It Happens to You" was co-written by Diane Warren for the documentary The Hunting Ground, which focuses on sexual assault crimes on college campuses in the U.S. The song holds special significance for Gaga, who has previously spoken up about her own experience being raped at 19 years old.

"She talked about her experiences and the pain she still feels years after this happened," Sandhu recalls of their first rehearsal. "She said, 'I want all of you to look into that camera and I want you to hurt.' ... 'This is gonna be the time that we heal, and we're gonna heal together.'"

See the interview in the player below.

WATCH: Lady Gaga 'Was Sobbing' at Oscar Performance Rehearsal, Told Sexual Assault Survivors 'We're Gonna Heal Together'