PW: When did you realize that you wanted to write The Long Goodbye?

Patti Davis: The full reality of my dad's Alzheimer's didn't hit me until a few months after his diagnosis. And I did what writers always do: I sat down to write. These journal entries were the only way I knew to make sense of what would be one of the most important journeys of my life. At first, I thought I was writing a magazine piece, but as my manuscript expanded, I realized I had a book on my hands. I stuck with the journal structure because it gave an immediacy to the story.

So you started writing in April 1995, then set the manuscript aside after a couple of hundred pages in February 1997, then added two final entries in 2004. What made you stop writing in 1997?

I took a break because it seemed that there was nothing new to say. When something happened over those seven years, I would write a magazine piece as a sort of postcard from the Reagan family. Then I picked up where I left off in the manuscript when my dad was really close to the end last June.

You write about maintaining your family's zone of privacy. Was that hard to work around as you wrote about your childhood and your father's illness?

As the disease progressed, we became more comfortable with it and more relaxed about revealing certain information that wouldn't compromise his dignity—for instance, that he had around the clock nursing care, that there was really no language anymore. The silence he'd fallen into became more bearable to talk about, and it became more important not to sugarcoat things. If I felt at all uncertain as I was writing, I'd read passages to my mother and ask if they were okay. When I gave her the galley, she said, "Normally, I read very quickly, but I'm deliberately reading your book slowly because I don't want it to end." I took that as a compliment.

What's your favorite part of the book?

I'm very hard on myself as a writer, but I really love this book because it's still so immediate and resonant for me—especially his last day. I read the audiobook all in one session, and I was fine until I got to that part. I choked up at the end and had to stop for a minute. Luckily, the guys in the sound booth were very understanding.

What was the hardest part to write?

Writing is never hard for me. If somebody had said to me, you're not allowed to write about this, I'd feel like I was in a straitjacket. It's all I know how to do. It's my lifeblood.

What do you have to say to families who are in the midst of their own long good-byes?

I'm just one person who has gone through it, but I learned to have reverence for three words: I don't know. Because I didn't know—how this was going to evolve, what was going to happen, how it would change us. I'd advise anyone in a similar position not to make any decisions about how they're going to feel. Just stay present and learn.