Listlessness of some in jacuzzi unnerving, on reflection (5)
I believe the answer is:
ennui
'listlessness' is the definition.
(I've seen this before)
'some in jacuzzi unnerving on reflection' is the wordplay.
'some in' indicates a hidden word.
'on reflection' is a reversal indicator.
'iunne' is hidden within 'jacuzzi unnerving'.
'iunne' backwards is 'ENNUI'.
'of' is the link.
(Other definitions for ennui that I've seen before include "World-weariness" , "Low interest rate" , "Feeling of listlessness" , "Feeling of disaffection" , "Boredom, tedium" .)