During stressful periods at work and in his personal life, Elon Musk would stay awake at night and vomit. He says working so hard has 'taken its toll.'

• Walter Isaacson's biography "Elon Musk" reveals the billionaire's struggles with stress.
• Musk's partners have described him staying up all night and vomiting.
• "I've been burning the candle at both ends with a flamethrower for a very long time," he told Isaacson.

Elon Musk may be the world's richest person, but his success has been accompanied by stress-related bouts of vomiting and insomnia, per Walter Isaacson's biography of the billionaire.

The man at the helm of six companies has often spoken about working long hours and sleeping on the Tesla factory floor. That appears to have taken a toll on his wellbeing.

"When he faced tortuous challenges, the strain would often keep him awake at night and make him vomit," Isaacson wrote in the book published Tuesday.

Isaacson's biography recounts how Musk was due to deliver a speech at the Royal Aeronautical Society in London in 2008 after two SpaceX rockets had blown up and he was divorcing his first wife. During this period, he also visited Aston Martin's CEO, who was dismissive of the EV movement, Isaacson wrote. Musk woke the next day with stomach pains, he added.

"He can pretend to like stress, but his stomach can't," Isaacson wrote.

The pain was so severe Musk had to visit a doctor who ruled out appendicitis. He then headed to a London nightclub to blow off some steam, per the biography. It was there he first met Talulah Riley, whom he married twice.

After the 2008 economic crisis, Tesla was on the brink of bankruptcy and Musk began asking friends and family for money to pay staff, the biography said. Isaacson wrote that in the middle of the night, Musk would flail around and sleep-talk to himself.

Riley told Isaacson she thought Musk was going to have a heart attack.

"He was having night terrors and just screaming in his sleep and clawing at me," she said. "It would go to his gut, and he would be screaming and retching. I would stand by the toilet and hold his head."

Grimes, with whom Musk has three children, also recounted the billionaire's sleep difficulties to Isaacson. In 2019, Tesla was again in need of money to keep operating, and its CEO was desperate for a plan to convince investors.

"Night after night, Musk sat upright on the edge of his bed next to Grimes, unable to sleep," Isaacson wrote.

"Every couple hours I would wake up, and he was just still sitting there, in the thinking man statue pose, just completely silent on the edge of the bed, " Grimes told the biographer.

As dawn came, Musk told her about his vision for Tesla's Autonomy Day.

And in the fall of 2021, Musk flew to Cabo San Lucas in Mexico for his brother's wife's birthday party. Grimes was DJing, but Musk stayed in his room and played the strategy game "Polytopia."

Isaacson wrote that Musk's "mood swings and depression were manifest as stomach pains" and the billionaire was throwing up and had heartburn. He cut the trip short and asked Isaacson if he knew any good doctors.

"I'm not super ok tbh," Musk texted Isaacson. "I've been burning the candle at both ends with a flamethrower for a very long time. It has taken its toll. I was very ill this weekend."

Musk did not immediately respond to Insider's request for comment made outside of normal working hours.