Tesla's share price plummeted today after embattled CEO Elon Musk gave an extraordinary interview during which he burst out in tears, asked for someone to take his job and admitted he relies on Ambien to sleep.

The 47-year-old is facing mounting pressure and an SEC investigation over a tweet sent last week claiming to have 'secured funding' to take Tesla private.

Today's interview with the New York Times is likely to increase that pressure after he admitted to a raft of personal problems, exhaustion and says his friends are concerned for his health.

Tesla shares ended the day down nine percent to $306 after a series of falls in the wake of the tweet and ensuing controversy, wiping around $5.5bn off the value of the company.

Musk described the past year as 'excruciating' and the 'most difficult and most painful year of his career'.

The interview also raises concerns about Musk's drug use. It claims the board is aware that he has occasionally used 'recreational drugs' and Musk himself admits to frequently relying on Ambien to sleep.

The paper also claims that Tesla's board is concerned about his posts on Twitter while under the influence of Ambien and have urged him to quit social media.

Additionally Musk denied he was 'on weed' or 'stoned' when he sent the tweet claiming to be taking Tesla private for a $420 share, although he acknowledged the value could be taken as a reference to marijuana. He said: 'It seemed like better karma at $420 than at $419. But I was not on weed, to be clear.'

Elon Musk, pictured with his musician girlfriend Grimes last month, revealed he was suffering the 'most difficult and painful year of his career' in an emotional interview

It has been claimed that company chiefs have been searching for a Tesla number two to help Musk manage his workload and approached Facebook's chief operating officer Sheryl Sandberg about the job.

Musk himself said there was 'no active search' and said he was not planning to resign his positions.

But he said: 'If you have anyone who can do a better job, please let me know. They can have the job.

'Is there someone who can do the job better? They can have the reins right now.'

In a statement the firm's board paid tribute to Musk's 'commitment and dedication to Tesla' and praised him for 'having hundreds of thousands of cars on the road that customers love' and 'employing tens of thousands of people around the world'.

The newspaper reported that Musk had 'alternated between laughter and tears' in the interview and said he had not taken more than a week off work since 2001.

Tesla shares dropped sharply in early trading, wiping billions off the value of the company

Tesla has approached Facebook executive Sheryl Sandberg (pictured) as they look to find a number two to share Elon Musk's workload, it has emerged

Musk, pictured last year unveiling the Roadster 2, has said someone else could take his job

He admitted he relied on medication to help him sleep, saying: 'It is often a choice of no sleep or Ambien.'

According to the New York Times article, board members have noticed that Ambien 'contributes' to his late-night Twitter posts. It says they are also 'aware' that he has occasionally used recreational drugs. Friends are also worried about his health.

The entrepreneur said: 'It's not been great, actually. I've had friends come by who are really concerned.'

He admitted he had rounded up from $419 to set the possible price, offering an approximate 20 per cent premium over the market value, but said: 'Weed is not helpful for productivity. There’s a reason for the word ‘stoned.’ You just sit there like a stone on weed.'

Describing his 'most painful year' Musk said he had nearly missed his brother Kimbal Musk's lavish wedding to environmental activist Christiana Wyly in Spain.

Kimbal officially married Christiana, the daughter of billionaire Sam Wyly, on April 7, but celebrated the event with around 300 guests at Greco-Roman ruins near Girona.

Elon Musk is estranged from his and Kimbal's father Errol, after he had a baby with his own stepdaughter - a woman who is 42 years his junior.

Musk branded the 72-year-old 'evil' and 'a terrible human being' saying his father had done 'almost every evil thing you can possibly think of'.

Elon Musk said he had nearly missed the wedding of his brother Kimbal (pictured in Spain)

Musk's latest troubles began when he tweeted on August 7 to say: 'Am considering taking Tesla private at $420. Funding secured.'

He said he wrote the tweet on the way to airport, saying: 'It seemed like better karma at $420 than at $419. But I was not on weed, to be clear.' He admitted no one had seen the post in advance.

The sudden announcement sent Tesla's share price rocketing by 11 per cent in one day, leading officials to ask if he had violated securities law by misleading investors about the funding.

The federal securities watchdog has sent Tesla subpoenas which typically indicates that it has opened a full formal investigation into a matter.

The company did not comment on that report, but it did say it was forming a special committee to evaluate proposals to take the company private.

On Monday, lawyers said Musk's statement indicated he had good reason to believe he had funding but seemed to have overstated its status by saying it was secured.

In a separate report, The Wall Street Journal said securities regulators have been investigating if Tesla misled investors about production problems for its Model 3 car.

Elon Musk's tweet saying he was considering taking Tesla private has sparked controversy

The company could face sanctions if regulators find it misled investors about production delays.

Musk also came under fire during the rescue of 12 children from a cave in Thailand where officials dismissed his plan to save them with a miniature submarine created by his rocket company SpaceX.

The billionaire was forced to apologise to British diver Vernon Unsworth, who helped to rescue the boys, after Musk labelled him 'pedo guy'.

Musk said he had built the submarine as an 'act of kindness' but said that his 'words were spoken in anger'.

He also came under fire when the Federal Election Commission released annual filings showing Musk as one of the top 50 donors to a political action committee dedicated to helping Republicans maintain control of the House.

While Musk has described himself as 'half Democrat, half Republican' in the past, critics said it was hypocritical of a green energy CEO to donate nearly $40,000 to the GOP.

A month earlier, in May this year, it emerged that Musk had launched an extraordinary outburst during a quarterly earnings conference call.

The billionaire branded one industry analyst a 'boring bonehead' during the bizarre session, saying another's 'questions are so dry they are killing me'.