Lessen stress by sorting out lack of sleep (12)
I believe the answer is:
restlessness
'lack of sleep' is the definition.
The definition and answer can be both states of affairs as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
'lessen stress by sorting out' is the wordplay.
'by' says to put letters next to each other.
'sorting out' indicates an anagram.
'lessen' put after 'stress' is 'stresslessen'.
'stresslessen' is an anagram of 'RESTLESSNESS'.
Can you help me to learn more?
(Other definitions for restlessness that I've seen before include "Agitation" , "Unease" , "Inability to keep still" , "Quality involving constant activity" , "Inability to relax -- lessen stress (anag)" .)