Really lacking in energy, on going uphill around hospital (3,4)
I believe the answer is:
not half
'really lacking' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.
'energy on going uphill around hospital' is the wordplay.
'energy on' becomes 'flat' (I can't explain this - if you can you should believe this answer much more).
'going' becomes 'on' (both can mean functioning or activated).
'uphill' is a reversal indicator (in a down clue, letters go up).
'around' means one lot of letters goes inside another.
'hospital' becomes 'H' (abbreviation for hospital).
'flat'+'on'='flaton'
'flaton' reversed gives 'notalf'.
'notalf' going around 'h' is 'NOT HALF'.
'in' is the link.
Can you help me to learn more?
(Other definitions for not half that I've seen before include "unequal share for you or me" , "Very much, greatly" , "anything except 50%" , "Very much, exceedingly" , "I couldn't agree more!" .)