all at once
happening or done quickly and without any warning

[TahlilGaran] Dictionary of Contemporary English ▲

all at once
1.
happening or done quickly and without any warning.
All at once I felt dizzy and had to lie down.

2.
at the same time.
I've had to deal with too many problems all at once.

[TahlilGaran] English Idioms Dictionary ▲

all at once
suddenly, without warning
All at once the fire alarm rang and we had to leave the building.

[TahlilGaran] English Idioms Dictionary ▲

all at once
adv. phr.
1. At the same time; together.
The teacher told the children to talk one at a time; if they all talked at one time, she could not understand them.
Bill can play the piano, sing, and lead his orchestra all at once.
2. or all of a sudden Without warning; abruptly; suddenly; unexpectedly.
All at once we heard a shot and the soldier fell to the ground.
All of a sudden the ship struck a rock.
Compare: AT ONCE.

[TahlilGaran] English Idioms Dictionary ▲