Biles, 24, later explained to reporters that she "had no idea where I was in the air," and that she was "having a little bit of the twisties."
That term is familiar to gymnasts, who know it as a phenomenon where they lose their understanding of where they are in the air, putting them at risk of injury when they land. Biles made that clear in her post-competition comments, saying, "I could have hurt myself."
Simone Biles at the team event
Carly Patterson, all-around gold medalist at the 2004 Athens Olympics, said during a Twitter Space hosted by PEOPLE on Thursday that she knew "exactly" what Biles was talking about.
"You basically start losing that air awareness," Patterson said. "It is very, very scary, especially when you're doing the difficult kind of skills that Simone is doing. [You] have no clue when you're going to hit the ground and how you're going to hit the ground."
Six-time All-American Katelyn Ohashi, who went viral for her floor routine as a gymnast for UCLA at the 2019 NCAA Championships, agreed, adding that the twisties are "not something to play with."
"She can't just go into a soft surface," Ohashi said, referencing how Biles could have landed off the mats. "When you have that doubt going into your head, anything can happen in that moment."
Biles has talked about struggling with the twisties before. In June, ahead of the Olympics, she said in an interview with Glamour that one of the toughest skills for her to learn has been a double-double flip on the floor, because she "would just get lost in the air."
"It took me a long time for my air awareness on that skill," she explained.
Biles' former coach, Aimee Boorman, said that Biles has experienced the twisties at other times in the 12 years that they worked together.
"Every once in a while, she would form this block and it usually had nothing to do with the gymnastics itself, it had to do with other things going on in her, in her universe," Boorman said on Today.
While Biles' decision to withdraw from the two events came as a shock, Patterson points out that you can't plan for the twisties: they just happen.
"Unfortunately it happened at the Olympic Games, it didn't happen three months ago when she could fix it, work those kinks out, work that mental block out," she says. "You can't do that in 24 hours, when you're at the Olympic Games, and rework your brain through that to really overcome it in such a short time."
"I'm so bummed and upset for her."
Biles and the three other members of Team USA — Jordan Chiles, Suni Lee and Grace McCallum — won silver at the team competition after her withdrawal, and Suni Lee nabbed gold in the all-around event on Thursday.
Simone Biles/Instagram Simone Biles, Sunisa Lee
The bronze medalist in the all-around, Russia's Angelina Melnikova, told reporters after the event that she's experienced the twisties too.
"I had similar problems when I was a kid and its really, really hard to get rid of this problem," she says. "It's very confusing and hard."
Biles may still compete, and is scheduled for the event finals in vault, floor, bars and beam on Sunday. She said she plans to take it "day by day," and see what she's able to do.
To learn more about Team USA, visit TeamUSA.org. Watch the Tokyo Olympics now on NBC.