The best possible long read article on the subject of what's happening in the markets and from a global macro economic POV is here: http://seekingalpha.com/article/3860226-sell-stocks-risk-ass...

What we're seeing the the beginning of a massive deleveraging as excess debt gets worked out of the system. It's possible that asset classes of all kinds (including startup valuations, real estate, stocks etc.) are 30-50% above par value. We'll see...