Occurring with no delay:
— Relief was instantaneous.

synonym: instant.

Roget 111: transient, transitory, transitive; passing, evanescent, fleeting, cursory, short-lived, ephemeral; flying etc. v.; fugacious, fugitive; shifting, slippery; spasmodic; instantaneous, momentaneous^†.    temporal, temporary; provisional, provisory; deciduous; perishable, mortal, precarious, unstable, insecure; impermanent.    brief, quick, brisk, extemporaneous, summary; pressed for time etc. (haste) 684; sudden, momentary etc. (instantaneous) 113.    ... show more

Roget 113: instantaneous, momentary, sudden, immediate, instant, abrupt, discontinuous, precipitous, precipitant, precipitate; subitaneous^†, hasty; quick as thought, quick as lightning, quick as a flash; rapid as electricity.    speedy, quick, fast, fleet, swift, lively, blitz; rapid (velocity) 274.    ... show more