He goes to clinic initially, twitching and feverish (6)
I believe the answer is:
hectic
'feverish' is the definition.
('hectic' can be a synonym of 'feverish')
'he goes to clinic initially twitching' is the wordplay.
'goes to' means one lot of letters go next to another.
'initially' suggests taking the first letters.
'twitching' becomes 'tic' (tic is a kind of twitching).
The initial letter of 'clinic' is 'c'.
'he'+'c'+'tic'='HECTIC'
'and' is the link.
(Other definitions for hectic that I've seen before include "Marked by intense agitation - fevered" , "Frantic or feverish" , "in a rush" , "Marked by intense activity" , "Extremely busy - fevered" .)