"Too expensive" does not equal bubble. It has to be expensive because speculators are driving the price up, thinking they're all fooling each other. As soon as they get get scared that the other speculators might be thinking of selling the price suddenly collapses as they race to not be the last to divest.
If something is expensive because it's scarce, is actually being practically used, and there are no substitutes, then there is no way to make the price suddenly collapse other than flooding the market with new supply, and it would take many years to increase the supply of housing by a significant percent. If the price of housing drops a bit all of the homeowners aren't going to rush to sell their homes in a panic like you might see with a purely speculative asset.