A decade ago, Hadley Vlahos was lost. She was a young single mother, searching for meaning and struggling to make ends meet while she navigated nursing school. After earning her degree, working in immediate care, she made the switch to hospice nursing and changed the path of her life. Vlahos, who is 31, found herself drawn to the uncanny, intense and often unexplainable emotional, physical and intellectual gray zones that come along with caring for those at the end of their lives, areas of uncertainty that she calls “the in-between.” That’s also the title of her first book, which was published this summer. “The In-Between: Unforgettable Encounters During Life’s Final Moments” is structured around her experiences — tragic, graceful, earthy and, at times, apparently supernatural — with 11 of her hospice patients, as well as her mother-in-law, who was also dying. The book has so far spent 13 weeks on the New York Times best-seller list. “It’s all been very surprising,” says Vlahos, who despite her newfound success as an author and her two-million-plus followers on social media, still works as a hospice nurse outside New Orleans. “But I think that people are seeing their loved ones in these stories.”

What should more people know about death? I think they should know what they want. I’ve been in more situations than you could imagine where people just don’t know. Do they want to be in a nursing home at the end or at home? Organ donation? Do you want to be buried or cremated? The issue is a little deeper here: Someone gets diagnosed with a terminal illness, and we have a culture where you have to “fight.” That’s the terminology we use: “Fight against it.” So the family won’t say, “Do you want to be buried or cremated?” because those are not fighting words. I have had situations where someone has had terminal cancer for three years, and they die, and I say: “Do they want to be buried or cremated? Because I’ve told the funeral home I’d call.” And the family goes, “I don’t know what they wanted.” I’m like, We’ve known about this for three years! But no one wants to say: “You are going to die. What do you want us to do?” It’s against that culture of “You’re going to beat this.”

Is it hard to let go of other people’s sadness and grief at the end of a day at work? Yeah. There’s this moment, especially when I’ve taken care of someone for a while, where I’ll walk outside and I’ll go fill up my gas tank and it’s like: Wow, all these other people have no idea that we just lost someone great. The world lost somebody great, and they’re getting a sandwich. It is this strange feeling. I take some time, and mentally I say: “Thank you for allowing me to take care of you. I really enjoyed taking care of you.” Because I think that they can hear me.

The idea in your book of “the in-between” is applied so starkly: It’s the time in a person’s life when they’re alive, but death is right there. But we’re all living in the in-between every single moment of our lives. We are.

So how might people be able to hold on to appreciation for that reality, even if we’re not medically near the end? It’s hard. I think it’s important to remind ourselves of it. It’s like, you read a book and you highlight it, but you have to pick it back up. You have to keep reading it. You have to. Until it really becomes a habit to think about it and acknowledge it.

Do these experiences feel religious to you? No, and that was one of the most convincing things for me. It does not matter what their background is — if they believe in nothing, if they are the most religious person, if they grew up in a different country, rich or poor. They all tell me the same things. And it’s not like a dream, which is what I think a lot of people think it is. Like, Oh, I went to sleep, and I had a dream. What it is instead is this overwhelming sense of peace. People feel this peace, and they will talk to me, just like you and I are talking, and then they will also talk to their deceased loved ones. I see that over and over again: They are not confused; there’s no change in their medications. Other hospice nurses, people who have been doing this longer than me, or physicians, we all believe in this.

But you’ve made a choice about what you believe. So what makes you believe it? I totally get it: People are like, I don’t know what you’re talking about. So, OK, medically someone’s at the end of their life. Many times — not all the time — there will be up to a minute between breaths. That can go on for hours. A lot of times there will be family there, and you’re pretty much just staring at someone being like, When is the last breath going to come? It’s stressful. What is so interesting to me is that almost everyone will know exactly when it is someone’s last breath. That moment. Not one minute later. We are somehow aware that a certain energy is not there. I’ve looked for different explanations, and a lot of the explanations do not match my experiences.

That reminds me of how people say someone just gives off a bad vibe. Oh, I totally believe in bad vibes.

But I think there must be subconscious cues that we’re picking up that we don’t know how to measure scientifically. That’s different from saying it’s supernatural. We might not know why, but there’s nothing magic going on. You don’t have any kind of doubts?

For the dying people who don’t experience what you describe — and especially their loved ones — is your book maybe setting them up to think, like: Did I do something wrong? Was my faith not strong enough? When I’m in the home, I will always prepare people for the worst-case scenario, which is that sometimes it looks like people might be close to going into a coma, and they haven’t seen anyone, and the family is extremely religious. I will talk to them and say, “In my own experience, only 30 percent of people can even communicate to us that they are seeing people.” So I try to be with my families and really prepare them for the worst-case scenario. But that is something I had to learn over time.

Have you thought about what a good death would be for you? I want to be at home. I want to have my immediate family come and go as they want, and I want a living funeral. I don’t want people to say, “This is my favorite memory of her,” when I’m gone. Come when I’m dying, and let’s talk about those memories together. There have been times when patients have shared with me that they just don’t think anyone cares about them. Then I’ll go to their funeral and listen to the most beautiful eulogies. I believe they can still hear it and are aware of it, but I’m also like, Gosh, I wish that before they died, they heard you say these things. That’s what I want.

You know, I have a really hard time with the supernatural aspects, but I think the work that you do is noble and valuable. There’s so much stuff we spend time thinking about and talking about that is less meaningful than what it means for those close to us to die. I have had so many people reach out to me who are just like you: “I don’t believe in the supernatural, but my grandfather went through this, and I appreciate getting more of an understanding. I feel like I’m not alone.” Even if they’re also like, “This is crazy,” people being able to feel not alone is valuable.

This interview has been edited and condensed for clarity from two conversations.

David Marchese is a staff writer for the magazine and the columnist for Talk. He recently interviewed Alok Vaid-Menon about transgender ordinariness, Joyce Carol Oates about immortality and Robert Downey Jr. about life after Marvel.