Disconcerted when it's overturned (5)
I believe the answer is:
upset
I believe this is a double definition.
'disconcerted' is the first definition.
(I've seen this in another clue)
'it's overturned' is the second definition.
(synonyms)
'when' is the link.
(Other definitions for upset that I've seen before include "bug" , "Overturn - worry" , "Make unhappy; disrupt" , "thrown?" , "Overturn; distress" .)