According to @StockMKTNewz, the S&P 500’s largest single-session losses include Oct 19, 1987 (-20.5%), Oct 28, 1929 (-12.3%), Mar 16, 2020 (-12.0%), Oct 29, 1929 (-10.2%), Nov 6, 1929 (-9.9%), Mar 12, 2020 (-9.5%), and Oct 18, 1937 (-9.3%) (source: @StockMKTNewz on X, Dec 28, 2025). The post presents these as part of the top 10 worst days in S&P 500 history, providing concrete reference points for historical drawdown risk sizing, stress testing, and volatility scenario planning across risk assets, including crypto (source: @StockMKTNewz on X, Dec 28, 2025).