Revel wildly in loch, lacking anxiety, perhaps (9)
I believe the answer is:
nerveless
'lacking anxiety perhaps' is the definition.
'revel wildly in loch' is the wordplay.
'wildly' indicates anagramming the letters.
'in' indicates putting letters inside.
'loch' becomes 'ness' (I've seen this before).
'revel' anagrammed gives 'rvele'.
'rvele' inserted inside 'ness' is 'NERVELESS'.
(Other definitions for nerveless that I've seen before include "Without fear" , "Not able to feel" , "no feeling" , "calm and collected" , "Showing calm self-control" .)