In/like a flash
Definition 1 of 1
Pro Tip 1/3Sudden Events
Use it when something happens unexpectedly and very quickly, like a surprise. 
The power went out in a flash during the storm.
Pro Tip 2/3Quick Actions
Ideal for describing very rapid actions or reactions, often within seconds. 
He caught the ball in a flash.
Pro Tip 3/3Informal Tone
It's casual and perfect for informal conversations, not for formal writing. 
I'll be back in a flash, don't worry!