Suddenness.
The state of being sudden.
Suddenly.
Happening quickly and without warning; hasty.
Mrs. Arnot gave a sudden sigh. – A Knight Of The Nineteenth Century by E. P. Roe
Of a sudden, she caught sight of an old woman moving about in among the trees. РJerusalem by Selma Lagerl̦f
I think not- But it was rather sudden. – The Ridin' Kid from Powder River by Henry Herbert Knibbs