Hayden Panettiere's Body 'Ballooned' After Her Brother's Death: 'I Lost Half Of My Soul'

"When my brother passed away, my body did something I've never really seen it do before which was within days," she said.

Hayden Panettiere is opening up about how her body reacted to the trauma of losing her brother suddenly.

The 35-year-old sat down with PEOPLE and shared the what happened just days after losing her younger brother Jansen to an undiagnosed enlarged heart.

"When my brother passed away, my body did something I've never really seen it do before which was within days," she told the publication.

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"I just ballooned out," she said of her rapid 40-pound weight gain. "It didn't matter what I did, what I ate. I know stress and cortisol running through your body can do that. Now I think my body was protecting itself, shielding itself from the world."

The grief she felt over the loss of her 28-year-old brother then triggered agoraphobia, where she was barely able to leave the house for months.

"I had to see horrific paparazzi pictures of myself coming out of Jansen's funeral, which happened in a very private place, and it was shocking," she said. "I didn't recognize myself. My agoraphobia came out, which is something I’ve struggled with in the past."

She said it affected her self esteem, adding, "It became a destructive hamster wheel of, do I feel good enough to go out?"

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However over time, she began to think about the prospect of going back to work and began walking and training with a PT, Marnie Alton.

"These long, beautiful walks where we could vent and it would be this therapy session," she says. "Marnie empowered me."

"My body just started reacting, not just from the working out. It allowed me to release the stress, the high expectations I'd always put on myself," she says. As her insecurities faded, so did her agoraphobia. "There's nothing like looking in the mirror and feeling like you look good enough to walk out the door," she said.

Although Panettiere is in a better place, the actress went onto share how heartbreaking the loss will always be for her.

"He was my only sibling, and it was my job to protect him," she said. "When I lost him, I felt like I lost half of my soul... I will always be heartbroken about [him], I will never be able to get over it. No matter how many years go by, I will never get over his loss."

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