Unconscious energy in lapse unfortunately (6)
I believe the answer is:
asleep
'unconscious' is the definition.
(associated in meaning)
'energy in lapse unfortunately' is the wordplay.
'energy' becomes 'e' (physics symbol as in E=mc2).
'in' means one lot of letters goes inside another.
'unfortunately' indicates an anagram (a bad or unfortunate spelling).
'lapse' anagrammed gives 'aslep'.
'e' put within 'aslep' is 'ASLEEP'.
(Other definitions for asleep that I've seen before include "Snoozing" , "Dormant, inactive" , "Dead to the world" , "Knitting up the ravelled sleeve of care" , "Conked out" .)