The S&P BSE Sensex surged 368 points on Friday, the recovery after 970-point fall in this week earlier, to a day's high of 37,489.24 tracking the strongness in Indian rupee value against US dollar, lower crude oil prices, government's directive to oil marketers to book future prices of crude oil and positive Asian cues. Shares of ICICI Bank, Reliance Industries, HDFC Bank, ITC, Axis Bank, HDFC and SBI were the biggest positive point contributors to the benchmark index, as these stocks collectively added about 350 points. 

What triggered the sudden fall in indian market ? From July to September 2018, 2 of IL& FS 256 subsidiaries reported having trouble paying back loans and intercorporate deposits to other banks and lenders , resulting in RBI requesting its major shareholders to rescue it . In July 2018 , Hindu Business line reported that the road arm of IL & FS was having difficulty making payments due on its bonds . In the same month , Business standard reported that it's founder Ravi Parthsarathy would be leaving the firm . In September Economic Times reported that one of the IL & FS group of companies called IL& FS Financial services limited had default on its commercial paper payments .This led to an audit by RBI . IL& FS Financial services limited had defaulted on repaying about 450 Cr worth of intercorporate deposits to Small industrial development bank of India ( SIDBI ) . This created panic in investors and they also doubted other arms of the IL&FS . This resulted in sudden fall in stocks related to financial institutions such as DHFL, Indiabulls housing finance , Canfin homes etc . Not only financial services stocks got butchered but other sectors such as infrastructure stocks also got plummeted as IL& FS deals with funding of many sectors .

Preparation is key. The best time to react to any potential market crash is before it occurs. Not after. Reacting in the moment can lead to expensive and costly mistakes. For example, if you saw that socks were on sale, you'd be more interested in buying socks. However, when it comes to stocks, people take a different view. When stocks are on sale, as can occur in a market crash, then often investors' instincts are to run away. Thinking about your strategy ahead of time and writing it down, just in a couple of paragraphs, can be key. Then if the markets do crash, make sure to look at that document before you act.
The crash on October 19, 1987, a date that is also known as Black Monday, was the climactic culmination of a market decline that had begun five days before on October 14. The DJIA fell 3.81 percent on October 14, followed by another 4.60 percent drop on Friday, October 16. On Black Monday, the Dow Jones Industrials Average plummeted 508 points, losing 22.6% of its value in one day. The S&P 500 dropped 20.4%, falling from 282.7 to 225.06. The NASDAQ Composite lost only 11.3%, not because of restraint on the part of sellers, but because the NASDAQ market system failed. Deluged with sell orders, many stocks on the NYSE faced trading halts and delays. Of the 2,257 NYSE-listed stocks, there were 195 trading delays and halts during the day.[27] The NASDAQ market fared much worse. Because of its reliance on a "market making" system that allowed market makers to withdraw from trading, liquidity in NASDAQ stocks dried up. Trading in many stocks encountered a pathological condition where the bid price for a stock exceeded the ask price. These "locked" conditions severely curtailed trading. On October 19, trading in Microsoft shares on the NASDAQ lasted a total of 54 minutes.
The May 6, 2010, Flash Crash,[1][2] also known as the Crash of 2:45, the 2010 Flash Crash or simply the Flash Crash, was a United States trillion-dollar[3] stock market crash, which started at 2:32 p.m. EDT and lasted for approximately 36 minutes.[4]:1 Stock indexes, such as the S&P 500, Dow Jones Industrial Average and Nasdaq Composite, collapsed and rebounded very rapidly.[4] The Dow Jones Industrial Average had its second biggest intraday point drop (from the opening) up to that point,[4] plunging 998.5 points (about 9%), most within minutes, only to recover a large part of the loss.[5][6] It was also the second-largest intraday point swing (difference between intraday high and intraday low) up to that point, at 1,010.14 points.[4][5][7][8] The prices of stocks, stock index futures, options and exchange-traded funds (ETFs) were volatile, thus trading volume spiked.[4]:3 A CFTC 2014 report described it as one of the most turbulent periods in the history of financial markets.[4]:1

Market crashes are far more common in our imagination than in reality. This is because they are vivid and scary events. Given our evolution, we are wired to worry about these sorts of vivid events. While, this may have been useful in helping us avoid getting eaten by tigers, it's less useful for rational, disciplined stock market investing. By thinking this topic through now, hopefully you're a little better prepared when the next crash hits.