U.S. stock markets have rebounded sharply, with the S&P 500 up nearly 6% and the Nasdaq Composite surging almost 9% in May, largely driven by robust gains in technology shares linked to artificial intelligence. Nvidia led the charge, rising over 23% in the month. However, analysts warn that valuations are high and earnings projections are still being revised downward, suggesting investors should remain cautious amid ongoing tariff uncertainties and elevated interest rates.