And back in the Spring of 1720, Sir Isaac Newton owned shares in the South Sea Company, the hottest stock in England. Sensing that the market was getting out of hand, the great physicist muttered that he "could calculate the motions of the heavenly bodies, but not the madness of the people." Newton dumped his South Sea shares , pocketing a 100% profit totaling £7,000. But just months later, swept up in the wild enthusiasm of the market, Newton jumped back in at a much higher price - and lost £20,000 (or more than $3 million in today's money). For the rest of his life, he forbade anyone to speak the words "South Sea" in his presence. John Carswell, The South Sea Bubble pp. 131, 199.

There was also the Tulip-Bulb Craze in the 1630s.

The amount the market declined from peak to bottom: This number is difficult to calculate, but, we can tell you that at the peak of the market, a person could trade a single tulip for an entire estate, and, at the bottom, one tulip was the price of a common onion.

And for those who think that real estate can never go down, there was the Florida Real Estate Craze of the 1920s.