Elon Musk, the chief executive of Tesla, and Arianna Huffington, co-founder of HuffPost, engaged in a public debate in recent days over how much sleep people need.

In an interview with The New York Times last week, Musk said that the last year had “been the most difficult and painful year of my career” as he struggled to meet Tesla’s production targets. He also revealed that he gets very little sleep, working up to 120 hours a week and relying on Ambien when he manages to squeeze in time for rest.

Getty Arianna Huffington (left), the co-founder of the HuffPost, is urging Elon Musk (right) to prioritize sleep in his life.

Huffington, author of the book “The Sleep Revolution” and founder of the wellness site Thrive Global, published an open letter to Musk that urged him to make sleep a priority.

“You’re a science and data-driven person,” Huffington wrote. “You’re obsessed with physics, engineering, with figuring out how things work. So apply that same passion for science not just to your products but to yourself. People are not machines. For machines ― whether of the First or Fourth Industrial Revolution variety ― downtime is a bug; for humans, downtime is a feature. The science is clear. And what it tells us is that there’s simply no way you can make good decisions and achieve your world-changing ambitions while running on empty.”

Dear Elon, please change the way you work to be more in line with the science around how humans are most effective: You need it, Tesla needs it and the world needs it. https://t.co/vy6hdnYKzt — Arianna Huffington (@ariannahuff) August 17, 2018

Musk tweeted his reply at 2:32 a.m. Sunday, per The Los Angeles Times: “Ford & Tesla are the only 2 American car companies to avoid bankruptcy. I just got home from the factory. You think this is an option. It is not.”

The tweet was later deleted, but Huffington apparently saw it.

In a statement to CNN, she said: “This is not about sleep, or about slowing down, or about asking Elon to chill out under a mango tree. It’s about how we can unlock and sustain our peak performance, and see solutions and opportunities where others can’t.”

Singer Kelly Clarkson also joined the discussion:

Well I can’t speak for him but I damn well needed to hear this 🤣🤣 I’m not an island and no one is. A rested mind is an evolving one. Thanks @ariannahuff this was like the best self help book/tweet ever, and it wasn’t even meant for me ha! https://t.co/yWykhnclsa — Kelly Clarkson (@kelly_clarkson) August 19, 2018