This rebound is necessary for:- the oversold of shares for past weeks resulted funds has to cover back by buying back shares that they do not own. Shares cannot be short sell to zero and not covered back. Borrow shares without returning is stealing. 

Rebound will not be very long as it's still a bear market, when the funds had their covering, it's just a matter of time, they use 'bad news' to short counters again.

True bull run will only come when Fed do a QE or when the valuation is appropriate and economy is recovering.

Key for now is:- taking the current plunge and May/June plunge to understand the bottoming of company share price movement. Buy into the dip.