When author Elizabeth Lesser discovered she was a match to donate bone marrow to her younger sister, Maggie, who was battling lymphoma, a flurry of thoughts raced through her mind. Would it work? Would it hurt? Would it be frightening?

I had a tremendous amount of mixed emotions, but mostly what I had was: what an honor, Lesser says. It was an honor.

Lesser opened up about the process of donating bone marrow during a conversation with Oprah on SuperSoul Sunday, admitting that although donating was an honor, it wasnt a painless one.

Theres a lot of pain leading up to it, Lesser says. In order to stimulate more stem cells to come out into the blood stream, they give you this growth factor that makes your bones ache tremendously. It happens over five days.

Regardless of any pain associated with bone marrow donation, Lesser knew immediately that it was what she was meant to do. You want to feel useful, you want to feel purposeful, you want to feel generous, she says. I mean, what could be easier, in a way? You just get blood taken out of you and you give it and you save someones life.

Lesser donated her marrow in 2013, however, the transplant did not save Maggies life. She died a year and a half later. Standing beside Maggie throughout her battle taught Lesser many things , one of which has been about the miracle of life that takes place inside our bodies. Right now, your stem cells are waiting for your body to say, I need new stem cells to come out through the bones and create new brain cells, new skin cells. Its a miracle, she says. Theres this amazing life and death dance going on, right now.

As for the bone marrow donation process, Lesser sums it up in one beautiful, profound sentence.

It was an amazing experience to feel that deep ache, she says.

Another experience of Lessers:

The visitation dream Lesser says she experienced two weeks after Maggies death