The Nasdaq 100 is heading for its best H1 ever, with a surge of 36% so far this year. But Wall Street is concerned that the rally may be derailed by the Federal Reserve tightening its policy. Despite recession fears and bank failures, investors have remained optimistic as the US economy shows resilience and the earnings outlook improves. However, analysts warn that the rally in tech stocks appears overblown due to rich valuations and only a few high-flying companies such as Apple, Microsoft and Nvidia. Historically, a strong first-half for the stock market has been a good omen for the rest of the year.