Author JK Rowling has revealed she often worries about dying before getting her stories published.
The Harry Potter creator said she has "loads" of ideas in her head, but is concerned time will run out, as she spoke to BBC Radio 2's Simon Mayo on his Drivetime show.
She said: "I sometimes genuinely worry that I'll die before writing them all out. That's my mid-life crisis, that I'll leave this earth without having written them all."
Rowling, who has written her third crime novel about veteran-turned-private investigator Cormoran Strike under the pseudonym Robert Galbraith, revealed some of her ideas include another children's book as well as novels for adults.
She said: "I have plans to write novels - in the plural - as JK Rowling again but I'm not going to give you an absolute date because things are busy enough. I have an idea for a children's book, which I really love - I've been writing part of a children's book so I'm going to finish that - and I have ideas for other adult books."
The 50-year-old, who has also been working on the script for a film adaptation of Fantastic Beasts And Where To Find Them, starring Eddie Redmayne, said she has more ideas for the Strike series.
"What's nice about the Strike books is I don't have an end point. I'm not as prescriptive as with the Potter books," she said.
"I could even probably go to 10, even beyond, I don't know, depending on the number of plots. What will ultimately limit it is the relationship between Striker and Robin (Ellacott, his investigator partner), and that's the through-line.
"I think at the point where I don't enjoy writing about them any more, that will probably be the point when Robert stops writing this series but I certainly am nowhere near that yet."
Rowling said she is still "disappointed" after being outed as Galbraith in 2013 by someone at the entertainment law firm Russell's, shortly after her first Strike novel, The Cuckoo's Calling, was published.
She said: "I wish Robert had lasted longer. It's unrealistic, but looking back, if I could have had three books... It felt a little premature. I felt a little disappointed.
"I was so grateful for what happened with Potter, but I'm the kind of writer who really wants to be alone in a room writing most of the time. This is fun, so Robert gets to have a lower key existence normally than I do. With Robert, it feels like it's about the writing even though people know it's me."
The novelist also laughed off any suggestions she has more pen names, saying: "Trying to run more than one pseudonym is a fool's game. I don't have the energy."
Rowling also revealed how she gave herself sleepless nights writing the third Strike book, Career Of Evil, which is out now.
"It's definitely the darkest of the series so far. It's the only book I've ever written that has given me literally nightmares," she said.
"I read a lot of police reports and accounts of serial killers. There are people who have done these sorts of things, I did a lot of research and that has disturbed me quite a lot. I also wanted to get into the killer's head."
The author also spoke about Harry Potter And The Cursed Child, which opens in the West End in June next year. The play, based on an original new story by Rowling, Jack Thorne and John Tiffany, is the eighth story in the Harry Potter series and is set 19 years on from the last book, Harry Potter And The Deathly Hallows.
She said: "It is really exciting. I personally had no particular desire to write it as a novel, for reasons that will become clear when people see the play.
"This play would never have happened if this particular team had never come to me. They're extraordinary, and together we're going to make a fantastic experience for people. I didn't go looking for this, this found me."