The economic explanation for this is quite simple: huge growth in the stock market means that money is being taken from productive and moved into speculative vehicles. The higher the growth in the stock market, the higher the desire to move more money into stock (the phenomenon of "chasing returns"). So, contrary to what most economists say, a high growth in the stock market is a primary indicator that the real economy is lacking investment. Of course the result is that a huge recession follows, which is "explained away" by economists as the "normal investment cycle".