Every asset bubble in history reverted to its mean. The mean would be the continuation of the pre-spike trendline. Let’s look at the NASDAQ, since you brought up that example.
The investors that I follow (Bill Fleckenstein, Barry Ritholtz at The Big Picture, Mr. Yamamoto, Zeal) say that stock market is still overvalued. The NASDAQ bubble certainly corrected. Look at this chart. It rose steadily for many years to reached a value of around 2000 in mid-1998, shot up to a high of 5046 on 3/9/2000, and then reverted back to its pre-spike value in mid-2001, and hasn’t budged since. It last closed at 2085. While I only lost $2K in tech stocks, I heard people telling me they lost hundreds of thousands, or even half of their retirement money. They have not earned it back.