The sadness when response is totally lacking (2,3)
I believe the answer is:
no joy
'the sadness when response is totally' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.
'lacking' is the wordplay.
I cannot really see how this works, but
'lacking' could be 'no' (I've seen this in other clues) and 'no' is found in the answer.
The remaining letters 'joy' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for no joy that I've seen before include "lack of success" , "Unsuccessful (colloq.)" .)