What is it like to watch a loved one die? What is it like to be the one dying?

In the National Geographic Channel documentary “I Am Dying,” we watch as Renee Heidtman — a spirited, active yoga instructor in her 20s — is first diagnosed with breast cancer. The film follows Renee and her family through her attempts to get treated, her final months of in-home care, and, finally, her death on April 11, 2013.

While unflinching in its depiction of the harsh realities of dying, the film is also a tender look at family and sisterhood.

“It’s really a story about love, family, and community,” says executive producer Mary Lisio, who worked with fellow producers Casey Affleck and Joaquin Phoenix to bring Renee’s story to the screen.

Along with footage filmed at Renee’s San Francisco home during her final weeks, the film also features some of the video diaries Renee shot herself. These diaries span from her diagnosis to her final weeks of life. In between, we see glimpses of her day-to-day life and her adventures on a road trip, as well as her attempts to treat the cancer holistically, and finally through chemotherapy.

Sifting through over 10 hours of personal footage, Lisio says she and the other filmmakers were struck by Renee’s optimism and strength: “We get to know Renee as a person not just defined by her illness, but as a person who is spirited, well-loved, and adventurous.”

“We all think of what we would do in that situation,” she says. “Seeing her smile and her hope and her optimism… She never gave up, and really believed in the course of treatment she’d chosen. She was really just a joyful person and made the best efforts to stay positive and project that positivity and hope.”

Renee received hospice care for a little less than six months. While she had the option to spend her remaining days in a hospital or care facility, Renee chose to be cared for at home.

“For someone like Renee, she would have felt alienated [being cared for elsewhere]. It wouldn’t have been a death that suited her character,” says her younger sister, Rita Heidtman, who took on the brunt of caregiving duties, helped by friends and other family members.

But, as it would have on any caregiver in her situation, she admits that the experience took an emotional and physical toll.

“It takes a lot of people to take care of one person, and a lot of the burden tends to go on one person,” says Rita, who was aided by friends, family members, and a team of nurses and caregivers from Sutter Care at Home. “It was mostly me, her friends, and our family taking care of Renee. That meant everything from medications, to changing clothes and diapers, to everything else.”

“Your family and friends are going to take care of you better than any other person,” says Rita. But still, the financial struggle was real. Beyond the hospital, there was rent, groceries, and other essentials to worry about — costs that any sick person would be hard-pressed to cover themselves.

“It’s difficult to for a single person to make do in that situation, when all you have are your disability checks,” says Rita. “Those checks are quite small.”

Fortunately, friends and family members were able to help, and Rita is especially thankful to people who donated to caregiving expenses on crowdfunding websites like GoFundMe.

With “I Am Dying,” Lisio says the filmmakers’ main goal is to showcase the realities of the ultimate shared experience: death.

“I think it certainly reminds us all that our time on this earth is precious,” she says, noting that everyone she has shown the film to has been quick to call loved ones and tell them how valued they are. “When they watch it, I’m hoping people think about what they would do in that situation, and use it as an opportunity to reflect back on life.”

“We wanted to show that positive things come out of death, too. It’s not just doom and gloom,” says Rita. “We’re hoping to show some light.”

“I Am Dying” first premiered on June 13, 2015 on the National Geographic Channel.