Elon Musk’s reign as the world’s first trillionaire could prove remarkably short-lived after a sharp sell-off in shares of SpaceX removed more than $150bn from his fortune in a single day.The billionaire entrepreneur, who crossed the $1tn wealth threshold earlier this month following SpaceX’s blockbuster stock market debut, has seen his net worth fall to an estimated $1.1tn after investors took profits from the newly listed company.According to Forbes estimates, Monday’s 16 per cent slump in SpaceX shares erased more than $152bn from Musk’s personal wealth, highlighting the extraordinary volatility that can accompany fortunes tied closely to publicly traded companies.The decline has prompted fresh questions over whether Mr Musk could soon lose his status as the world’s only trillionaire if the weakness in SpaceX shares continues.SpaceX stock closed at $156 on Tuesday, slightly above the $150 level at which it began trading on 12 June but well below the record high of $225 reached just a week ago. The company’s initial public offering was priced at $135 a share, meaning investors who participated in the flotation remain in profit despite the recent retreat.The pullback has nevertheless been dramatic. At its peak, SpaceX was valued at almost $3tn, briefly becoming one of the most valuable companies in the world. Its market capitalisation has since fallen to just over $2tn, wiping away nearly $1tn in value in little more than a week.That decline alone is almost equivalent to Mr Musk’s entire fortune.(Getty Images)Danni Hewson, head of financial analysis at AJ Bell, said the sell-off reflected the reality that newly listed companies often experience a period of intense volatility after the initial excitement fades.“SpaceX might have seemed charmed after its record-breaking IPO and subsequent rally, but it’s come down to earth with a bump over the past couple of days, with shares at one point falling below the opening price on its market debut,” she said.“Post-IPO stocks often enter a period of volatility as the market gets to grips with the new entrant, some investors rush to cash out, and others assess at what price they are willing to jump in.“For a stock like SpaceX, a lot of decision making might have been emotional and based on the anticipation of huge leaps forward in space exploration and utilisation, but investing should be something treated with clear eyes and patience, even when such huge numbers are involved.”The pressure on SpaceX came alongside broader weakness across the technology sector. Tesla, another cornerstone of Mr Musk’s wealth, fell 5.8 per cent on Monday as investors sold off artificial intelligence and semiconductor-related stocks.Because much of Mr Musk’s wealth is concentrated in his corporate holdings rather than cash, fluctuations in the share prices of SpaceX and Tesla can cause enormous swings in his net worth from one day to the next.For now, the billionaire remains comfortably above the trillion-dollar mark. However, with his fortune having already fallen by around $200bn from its recent peak, further declines in SpaceX shares could rapidly bring the unprecedented milestone back into question.A further fall of roughly 10 per cent in Mr Musk’s wealth would be enough to push him below the $1tn threshold once again, underlining just how dependent the title of “world’s first trillionaire” remains on the mood of the stock market.The episode serves as a reminder that even at the highest reaches of global wealth, fortunes can rise and fall by sums larger than the annual economic output of many countries.