A gap-down happens when a stock opens at a much lower price than where it closed the day before, leaving a ‘gap’ on the price chart that’s considered a sign of investor panic. The Sensex and Nifty fell 1.5% the next day. A gap-down happens when a stock opens at a much lower price than where it closed the day before, leaving a ‘gap’ on the price chart that’s considered a sign of investor panic. The Sensex and Nifty fell 1.5% the next day. Economic Times