The stock market is an important part of the financial system because it provides companies with an opportunity to raise capital and gives investors a platform to invest their savings. However, stock prices do not remain constant. They continuously move in response to economic conditions, company performance, government policies, global events, interest rates, inflation, investor sentiment, and other factors. These changes can strongly influence the way investors think and act. The present study examines how investors respond to market fluctuations with reference to Kotak Securities in Chennai. Particular attention is given to investment decisions, risk perception, investor confidence, fear, financial knowledge, investment experience, and sources of market information. The study follows a descriptive and analytical research design and is based on primary data collected from 100 respondents through a structured questionnaire. Percentage analysis, frequency analysis, weighted average, correlation analysis, descriptive statistics, and Chi-square testing are used to understand investor behaviour. The findings indicate that market fluctuations have a noticeable influence on investment decisions. A weighted average score of 3.78 shows that respondents generally agree that market fluctuations affect their investment decisions. Sudden changes in stock prices also influence investors, with the highest proportion of respondents stating that such changes often affect their decisions. The study further shows that fear is an important emotional factor, while financial websites and applications are a major source of investment information. The correlation results indicate meaningful relationships among risk perception, market impact, fear, and investor confidence. The study highlights the importance of financial awareness, reliable information, disciplined decision-making, and professional support during periods of market uncertainty.