Consider an individual company. Or, a portfolio of companies.
At discount rate of 10%, and growth rate of 4%, one dollar of yearly income is worth 18.3 USD. (If you want the formula, open GNU Octave or Matlab and type
sum(1.04.^[0:1000] ./ 1.10.^[0:1000]) into it).
Now, if this year, income drops by 20%, instead of getting 1 USD, you get 0.8 USD, the company (or portfolio of companies) is worth 18.1 USD.
According to this calculation, a temporary 20% drop to gross domestic product should cause an approximately 1% drop in stock prices (18.1 / 18.3 = 0.989 so more precisely it's 1.1% drop).
Yet, stocks have fallen over 25%.
That doesn't make sense to me.
For some reasons, investors have panicked. They should not have panicked.
Now the recent rise in stock prices from the bottom just is due to slightly lessened panic.
That still doesn't change the situation that stocks are 25% cheaper than they used to be.