I read this great book when I was 10 called "Extraordinary Popular Delusions And The Madness Of Crowds". It's a classic of western non fiction and was published mid 19th century. Ever since, I have always noticed how quickly a short trend becomes a full-out mania or fear.
Just found the text of this great book:
http://www.litrix.com/madraven/madne001.htm
What I have remembered my whole life was the chapter on the tulipmania of Holland in the 1600's. Here is the chapter:
http://www.litrix.com/madraven/madne004.htm