Not yet in bed, drunk and unable to relax (7)
I believe the answer is:
uptight
'unable to relax' is the definition.
(I've seen this before)
'not yet in bed drunk' is the wordplay.
'not yet in bed' becomes 'up' (still up or awake).
'drunk' becomes 'tight' (slang term).
'up'+'tight'='UPTIGHT'
'and' acts as a link.
(Other definitions for uptight that I've seen before include "Highly-strung" , "Informally nervous and tense" , "Tense, nervous, repressed" , "Nervously tense or stressed" , "Repressed and disapproving" .)