A hot market can produce a surge of business for a short period of time, especially if you get in at the beginning. That's when sales are easy to get because the market is growing and there isn't much competition. Later, it becomes more difficult and expensive to get sales as more competitors flood into the market. Hot markets become highly competitive.
Most hot markets won't vanish like the Y2K market. A hot market may be a permanent market but the extraordinary profit potential it offers is temporary. It's difficult to build a permanent business based exclusively on a hot market. But you can use it as a temporary opportunity to launch a new business or to increase the profits of your existing business.