Switching gas, guy losing heart and drooping (5)
I believe the answer is:
saggy
'drooping' is the definition.
(I've seen this in another clue)
'switching gas guy losing heart' is the wordplay.
'switching' says the letters should be written backwards (switching direction).
'losing heart' suggests removing the centre.
'guy' with its middle removed is 'gy'.
'gas' back-to-front is 'sag'.
'sag'+'gy'='SAGGY'
'and' acts as a link.
(Other definitions for saggy that I've seen before include "Hanging down" , "Drooping" .)