Don't lean over as much when lacking energy (8)
I believe the answer is:
listless
'lacking energy' is the definition.
(I've seen this before)
'don't lean over' is the wordplay.
'don't' becomes 'less' (I can't explain this - if you can you should give a lot more credence to this answer).
'lean' becomes 'list' (both can mean to tilt).
'over' says to put letters next to each other (in a down clue, some letters go over others).
'less' after 'list' is 'LISTLESS'.
'as much when' acts as a link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for listless that I've seen before include "Devoid of spirit or energy" , "Lacking enthusiasm or energy" , "Showing no enthusiasm, torpid" , "Short of energy (and ill-equipped for shopping?)" , "Devoid of energy or concern" .)