I was VP Tech at a high profile ad driven startup. We raised $50M (Softbank money in those days). Spent a lot of it scaling up on Sun hardware, ran TV ads, saw tremendous response, then a week later the bottom in the ads business model dropped out. Literally a week later. Amazing.
We went from close to 300 staff in March (60 of which reported to me) to 7 in October. The CEO handled the layoffs.
Most of the developers who reported to me took months to find new jobs.
Many of the non-tech people who had found unique jobs in our business were not able to find similar work again and went to business school or law school.
I had worked day and night to scale up, then worked day and night to scale down. I burned out. I moved, stopped working for pay, lived on savings, went to grad school (in CS) for a while, then finally got back on the horse in 2005.
Some advice- worrying about the next bubble bursting is a distraction, like following the shiny. It is good you are asking the question, but the right plan to be making- a career plan- is what is important, and whether there is a bubble or not is kind of irrelevant.
You might lose your job in the midst of major investment, or you might weather repeated rounds of layoffs. Random things will happen uniquely to YOU. They have to all of us.
The average story is helpful context but it is not your story. Protect and defend yourself. You are the only one who can.