At home wearing headgear, having turned back flap (5)
I believe the answer is:
panic
'flap' is the definition.
(I've seen this in another clue)
'at home wearing headgear having turned back' is the wordplay.
'at home' becomes 'in' ('I'm in' can mean 'I'm at home').
'wearing' indicates putting letters inside.
'headgear' becomes 'cap' (cap is a kind of headgear).
'having turned back' says the letters should be written in reverse.
'in' placed into 'cap' is 'cinap'.
'cinap' back-to-front is 'PANIC'.
(Other definitions for panic that I've seen before include "Widespread fear" , "Lose one's cool" , "Mass fear" , "Agitation" , "Great consternation" .)