"That was definitely rock bottom for me," she says.
Bundchen reveals the panic attacks were brought on by a traumatizing incident when she was on a six-seater plane in Costa Rica and experienced severe turbulence.
"It started this fear of being in small spaces," she explains. "So, it started with a little plane ride but then it became like, tunnels, subways, elevators. ... My world just kept getting smaller and smaller."
Bundchen says one panic attack was so severe, she considered jumping off the balcony when she lived in an apartment on the ninth floor.
"It was like, I was trapped, and I couldn't breathe, even from outside my own balcony," Bundchen recalls, breaking down in tears. "From that moment on, I realized my life needed to change."
The supermodel then underwent a lifestyle change, trading in cigarettes, wine and sugary coffee drinks for a clean, plant-based diet she and husband Tom Brady have now become known for. She also practices meditation and yoga.
"Somebody told me a quote that I thought was fantastic one time: 'The mind is an instrument, don't let it play you,'" she says.
As for her relationship with 41-year-old Brady, the legendary quarterback of the New England Patriots, she says she's learned to "take a breath" from him.
"He's very calm and very centered," she notes. "And I feel like, you know, I'm very emotional and very changeable."
"I've never seen someone love something as much as he loves football, and it makes me happy," she says. "If I said anything in the past it's because ... you have a concern."
"I'm like, you know, no one is going to hurt someone I love. You know?" she adds about her attitude when it comes to her family. "You just feel very protective of them. So, obviously, if someone hurts my children, my husband, anyone I love, I get like a lioness."