Since the forex market is a free and unregulated market. The dynamics of forex is shaped and dictated by the flow of orders and the market conditions of supply and demand. National banks sometimes interfere to correct and modify unwanted exchange rate fluctuations in its nation's currency.
As opposed to the stocks, the forex currencies can not go down simultaneously because they trade in pairs against each other. Therefore, there always be a winner which differs from stocks, where in theory all stocks in a given market can move down (the bear market crash scenario).
This is why the SEC(Securities and Exchange Commission) has instituted such strict short selling rules on stocks. Overall, the greater freedom that the forex market permits traders tends to make the forex market very efficient and allows traders to profit equally and easily from either “bull markets” or “bear markets” that may be prevailing in one or more currency pairs
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