Without warning disorder alas unfolded (3,2,1,6)
I believe the answer is:
all of a sudden
'without warning' is the definition.
(I've seen this before)
'disorder alas unfolded' is the wordplay.
'disorder' is an anagram indicator (I've seen 'diseased' mean this (I've seen this in other clues)).
'alas'+'unfolded'='alasunfolded'
'alasunfolded' with letters rearranged gives 'ALL OF A SUDDEN'.
(Other definitions for all of a sudden that I've seen before include "abruptly" , "In an unexpected manner" , "Quickly and unexpectedly" , "Without warning" .)