Now so upset as to faint (5)
I believe the answer is:
swoon
'to faint' is the definition.
('swoon' can be a synonym of 'faint')
'now so upset' is the wordplay.
'upset' indicates anagramming the letters.
'now'+'so'='nowso'
'nowso' anagrammed gives 'SWOON'.
'as' is the link.
(Other definitions for swoon that I've seen before include "Faint (with emotion)" , "Fall fainting" , "Lose consciousness" , "Display of extreme emotion" , "Pass out" .)