If you being a trillionaire (perhaps even a billionaire were're talking about Musk) relies entirely on overinflated market valuation ans not your actual physical assets value, then you don't have that money.

You do realize that you can become a trillionaire for a day either, don't you? Just create a company, enter the market, emit gazillion actions and convince someone to buy it from you for a couple of bucks. Boom, all your gazillion actions are now worth that money. Try to avoid tax office at this point though.