Without energy, again experience ease (7)
I believe the answer is:
relieve
'ease' is the definition.
('relieve' can be a synonym of 'ease')
'without energy again experience' is the wordplay.
'without' is an insertion indicator.
'energy' becomes 'e' (physics symbol as in E=mci).
'again' becomes 're'.
'experience' becomes 'live' (living is a kind of experiencing**).
're'+'live'='relive'
'e' put within 'relive' is 'RELIEVE'.
(Other definitions for relieve that I've seen before include "Free someone from duty by taking his place" , "Assuage, ease" , "help" , "Soothe" , "cure" .)