Nurse in working life losing some energy (5)
I believe the answer is:
carer
'nurse' is the definition.
(I've seen this before)
'working life losing some energy' is the wordplay.
'working life' becomes 'career' (I've seen this before).
'losing' indicates named letters should be taken away.
'some energy' becomes 'e' (physics symbol as in E=mc2).
'career' with 'e' taken away is 'CARER'.
'in' acts as a link.
(Other definitions for carer that I've seen before include "Invalid's attendant" , "One attending invalid" , "One looking after another" , "Racer (anag.)" , "Person who attends to a dependent adult" .)