Snap is used in this sense. Usually as "like a snap". It is related to how quick finger snapping is.
(n) a quick, sudden action or movement, as the breaking of a twig.
As a phrase, there is just like that:
Suddenly and, sometimes, unexpectedly.
For example, The alarm went off, just like that , or And then they walked out, just like that .
As an adjective there is momentary (and its synonyms)
lasting for a markedly brief time; "a fleeting glance"; "fugitive hours"; "rapid momentaneous association of things that meet and pass"; "a momentary glimpse"