Hey Presto posted while I was still typing. And we agree on that "in a flash" means quickly.If you mean it can happen easily, then "in a breeze" or "in a light breeze" (a sailing metaphor, I believe) works fine. Like Sparky I find this a little-used metaphor, but one dictionary I consulted online lists its meaning:
in a breeze
Easily;handily;without much or any effort.
If you mean that it can happen very quickly, then "in a flash".
I agree. The sounds decidedly odd when referring a stock market. It's usually used in reference to people doing something effortlessly.To me, 'a breeze' is something that is done easily but not necessarily quickly. It doesn't quite work in your sentence.
Something like '' . . . go down in a flash/an instant' is more idiomatic.