Elon Musk repeatedly broke down in an interview in which he attempted to explain some of his recent strange behaviour.

The Tesla boss has admitted to taking pills to sleep and that he has had a difficult year, alternating between laughter and crying as he did.

And he revealed that the stress of the year appears to be undermining his physical health. "It’s not been great, actually. I’ve had friends come by who are really concerned," he said.

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Mr Musk made the revelations in an interview with the New York Times that appeared to have been organised primarily to address the controversy around a recent tweet he posted about Tesla.

He set off excitement and scandal around the financial markets and tech world when he posted on Twitter that he was planning to take Tesla private, a decision that would mark a major moment for the company, and that he had the money to do so.

"Am considering taking Tesla private at $420," he wrote on Twitter. "Funding secured."

But it soon became clear that the tweet had not been run by other parts of the company and that funding was not as secure as had been suggested. Regulators are now looking into the tweet, which caused panic in the financial markets and forced Tesla to make clear that it had only had discussions with potential investors about paying for a buyout.

He said that he had posted the tweet while he was driving to the airport. Doing so was an attempt at transparency, he claimed.

One of the more unusual parts of the tweet was the choice of the number 420, which has become a code for consuming cannabis. But Mr Musk said that was simply a coincidence: he had wanted to announce a number that was 20 per cent higher than its current price, he said, but $419 was an ugly number and so he had rounded up.

"It seemed like better karma at $420 than at $419,” he said in the interview. “But I was not on weed, to be clear. Weed is not helpful for productivity. There’s a reason for the word ‘stoned.’ You just sit there like a stone on weed."

But he did admit to using pills to go to sleep, often taking Ambien. "“It is often a choice of no sleep or Ambien,” he told the New York Times.

And the paper reported that board members are concerned that the drug doesn't always work to help Mr Musk sleep but instead fuels the late-night tweets in which he often makes some of his more unusual or controversial statements. The paper also suggested that board members believe Mr Musk also occasionally takes other recreational drugs – an allegation made recently by rapper Azaelia Banks, but which has been strenuously denied by Mr Musk's companies.

Much of Mr Musk's tough year has come as a result of increased pressure on Tesla to manufacture enough cars. That has led to its boss sleeping in the factory to ensure it is done, which in turn meant that he has nearly missed his brother's wedding, failed to see friends and spending several days without going outside at all, he said through tears.

That pressure has led to him working 120 hour weeks, he said. The Tesla boss has cited his intense work schedule and failure to sleep in explanation for other controversies before, including a recent moment in which he had attacked analysts for asking difficult questions during an investor call.

Mr Musk he did not address all of the controversies that made the year quite so excruciating. He did not discuss his much publicised intrusion into the rescue of the Thai boys from a cave, for instance, or the strange tweets he sent afterwards in which he attacked one of the divers who actually did with a series of lurid and baseless allegations.

He also said that he has no plans to give up his dual roles as chairman and CEO of Tesla, despite the fact that many of its investors would prefer him to. But he said that if a better person could be found than him, he would hand over power.