Very busy — fevered (6)
I believe the answer is:
hectic
I believe this clue is a double definition.
'very busy' is the first definition.
(I've seen this before)
'fevered' is the second definition.
(thesaurus)
(Other definitions for hectic that I've seen before include "Bustling" , "Feverishly busy" , "'Excited, flustered or rushed (6)'" , "Exciting, and confusing perhaps" , "'Rushed, madly busy (6)'" .)