Stomach-turning jerk (3)
I believe the answer is:
tug
'jerk' is the definition.
(I've seen this before)
'stomach-turning' is the wordplay.
'stomach' becomes 'gut' (I've seen this before).
'turning' is a reversal indicator.
'gut' in reverse letter order is 'TUG'.
(Other definitions for tug that I've seen before include "Pull jerkily" , "Pull hard or suddenly" , "draw with some effort" , "Pull; loop on saddle" , "Pull vigorously at or tow" .)