Tesla CEO Elon Musk opened up about “the most difficult and painful” year of his career in an interview with The New York Times in which he reportedly fought back tears. The billionaire told the Times that he has been working up to 120 hours a week at some points. “There were times when I didn’t leave the factory for three or four days—days when I didn’t go outside,” he was quoted as saying. “This has really come at the expense of seeing my kids. And seeing friends.” The pressure of the job has reportedly affected his health so severely that friends are growing concerned, and efforts are being made at the company to find him a No. 2 executive, according to the report. Some board members have also reportedly grown concerned over Musk’s alleged use of Ambien. Musk also commented on the recent scandal surrounding his Twitter announcement that he had “funding secured” to take Tesla private at $420 a share—a claim federal investigators are now probing to determine whether it was deliberately made to boost share prices. Musk told the Times he does not regret the tweet and that he’d chosen the $420 figure because “it seemed like better karma at $420 than at $419,” which was where stock had recently been trading. “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,” he said.