while surprised; suddenly; before one knows it
Describes something happening so quickly or unexpectedly that one is caught off guard. Often used in the set phrase あれよあれよという間に (in the blink of an eye).
See also: あれよあれよという間に (あれよあれよというまに) · あれよあれよといううちに
あれよあれよという間に、彼は社長になった。
Before anyone knew it, he became the company president.
Suddenly, a line had formed.