Disinterested, alternatively, in bed (5)
I believe the answer is:
bored
'disinterested' is the definition.
(thesaurus)
'alternatively in bed' is the wordplay.
'alternatively' becomes 'or'.
'in' means one lot of letters goes inside another.
'or' put into 'bed' is 'BORED'.
(Other definitions for bored that I've seen before include "Filled with ennui" , "Wearied by tedium" , "Short of things to do, maybe" , "Drilled; wearied" , "Unstimulated" .)