very fast; in a flash; before one's eyes
Describes a visible, often dramatic change happening rapidly right in front of the speaker. Commonly used with verbs of change like 変わる, 増える, 減る, 治る, etc.
After taking the medicine, my fever went down very fast.
The sky darkened before our eyes and a heavy rain started falling.
The wound visibly shrank right before our eyes.
The water was rapidly rising right in front of us.
My savings were visibly disappearing before my eyes.
His condition improved rapidly right before our eyes.