Went back, being lost? (4)
I believe the answer is:
deep
'being lost?' is the definition.
(thesaurus)
'went back' is the wordplay.
'went' becomes 'peed' (both can mean urinated).
'back' shows that the letters should be reversed in order.
'peed' written backwards gives 'DEEP'.
(Other definitions for deep that I've seen before include "profoundly" , "Sunk low" , "hard to understand" , "down a long way" , "Profound - engrossed" .)