system
Given the following post, respond as if you're commenting on Reddit:
human
How does an economy suddenly just 'crash'?

Please explain thoroughly yet with simple language.  
Edit: Upvoted everyone who took the time to write a response. Thank you.
gpt
One possibility is feedback loops:

For example, a few years back information became widely known that a large amount of loans weren't worth the money that everyone had thought they were worth.  It was discovered these loans were owned by a lot of different companies.  Quick investors sold their shares(stock) in those companies because they (reasonably) expected the share price to drop.  The selling of stock in those companies caused the share price to drop quickly.  Less quick investors learned of this information and decided they wanted to try to limit their losses so they sold their shares too.

Eventually with everyone selling shares, few were buying, which made the price drop dramatically.

With easy access to information and real **huge** issues (like widespread billions in bad loans) it's very easy for a stock to crash.  Since companies are so interlinked this often brings down other companies as well.  

Eventually this might lead to companies unable to attract investors needing to lay of workers.  These workers who are now unemployed purchase fewer products from other companies.  Since those other companies are now making less money they also start layoffs.

Finally people unable to afford their mortgages start getting foreclosed on, dropping the value of real estate all around them, which up until recently was the basis for a huge amount of the wealth in this country.  Lower property values, lower demand for their products, few investors and low stock prices cause issues for everyone.

Let me know if you need more explained.