Swallow sheltering is tense and agitated (10)
I believe the answer is:
distraught
'agitated' is the definition.
(similar in meaning)
'swallow sheltering is tense' is the wordplay.
'swallow' becomes 'draught' (draught is a kind of swallow).
'sheltering' means one lot of letters goes inside another.
'tense' becomes 't' (grammatical abbreviation).
'is'+'t'='ist'
'draught' enclosing 'ist' is 'DISTRAUGHT'.
'and' is the link.
(Other definitions for distraught that I've seen before include "Deeply agitated" , "wild" , "Beside oneself" , "Having got the wind up" , "crazy" .)