Ideas fester for Amy Sewell — they get into her head and she can’t let them go until she writes about them. That’s how it happened with “Mad Hot Ballroom,” her story about local kids learning ballroom dancing at PS 150 that she wrote for the Tribeca Trib and then turned into a documentary in 2005. And that’s how it is now with her recently self-published novel “Pocket8s.”

The topics this time: euthanasia and poker. (And coming up: guns, addiction and guilt.)

“My books are therapeutic — for me,” Amy said. “I write about things that bug me, and not in an irritating way but in a way that I think about them all the time. The questions always are, ‘if I was in their shoes, what would I do?’ And rather than answer them, I like to put them in a fictional situation.”

Amy, who’s lived in Tribeca since 1992 and raised her two daughters here, has published two non-fiction books and has been writing forever — she wrote her first poem at age 6 (she’s 59) and decided then to be a writer. (“My father told me I would starve, and he was probably right.”) She has always juggled her day jobs with her writing career, balancing one or the other on top. For “Pocket8s,” her non-fiction agent couldn’t help her with the marketing so she studied the self-publishing landscape, and engaged freelance editors, publicists and cover artists to move things along.

The novel is a psychological thriller about a lone gambler — a woman named Dutch — who is also in the risky business of euthanizing the terminally ill. When she is called home by her childhood friend for her services, she faces the toughest job of her career, forcing her to revisit and reckon with a messy past. Amy pulled from real life in this case — her mother-in-law, who died in 2016, was a euthanasia advocate and got her thinking about the subject; Amy and her husband are regular poker players, as is Dutch.

Her books take years to develop — her first table of contents for “Pocket8s” was sketched out in 2008 — and she likes it that way. She likes living with them for a while. She’s still wondering about Dutch. Is she a psychopath? Or is she the most compassionate person ever?

Her second novel, “The Hole in the Rabbit,” has just wrapped up, and she has two others in the pipeline vying for her attention. She describes her own novels as accessible with good storytelling, which is her forte — and her obsession.

“I am addicted to writing, to fiction — my mind thinks in scenes all day long, so I just keep going back to it,” Amy said. “In general I have no expectations, the achievement is in getting it birthed. I just find I am happier because of it.”